Secondary binding site of dipeptidyl peptidase IV (DPIV)

ABSTRACT

The present application relates to the secondary binding site of dipeptidyl peptidase IV, its relationship amongst substrates and to the modulation of substrate specificity of dipeptidyl peptidase IV (DP IV, synonym: DPP IV, CD26, EC 3.4.14.5). The application relates further to compounds that bind to the secondary binding site of DP IV and their use to modulate the substrate specificity of DP IV; methods of treatment of various DP IV mediated disorders; and screening methods for the identification of secondary binding sites on DP IV and DP IV-like enzymes.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims priority of U.S. patent application Ser. No.10/246,817, filed Sep. 18, 2002 and also claims priority of U.S.Provisional Patent Application Ser. No. 60/443,417 filed Jan. 29, 2003both of which are incorporated herein by reference in their entirety.

FIELD OF THE APPLICATION

The present application relates to the secondary binding site ofdipeptidyl peptidase IV, its relationship with any type of substratesand to the modulation of substrate specificity of dipeptidyl peptidaseIV (DP IV, synonym: DPP IV, CD26, EC 3.4.14.5).

The application relates further to compounds that bind to the secondarybinding site of DP IV and their use to modulate the substratespecificity of DP IV.

Furthermore, the present invention provides a method for treating DP IVmediated disorders, selected from but not restricted to, impairedglucose tolerance, glucosuria, lipid disorders, dyslipidemia,hyperlipidaemia, hypertriglyceridemia, hypercholesterolemia, low HDLlevels, high LDL levels, metabolic acidosis, hyperglycemia, diabetesmellitus, diabetic neuropathy and nephropathy and of sequelae caused bydiabetes mellitus in mammals, metabolism-related hypertension andcardiovascular sequelae caused by hypertension in mammals, for theprophylaxis or treatment of skin diseases and diseases of the mucosae,autoimmune diseases and inflammatory conditions, and for the treatmentof psychosomatic, neuropsychiatric and depressive illnesses, such asanxiety, depression, sleep disorders, chronic fatigue, schizophrenia,epilepsy, nutritional disorders, spasm and chronic pain, atherosclerosisand its sequelae, vascular restenosis, irritable bowel syndrome,inflammatory bowel disease, including Crohn's disease and ulcerativecolitis, other inflammatory conditions, pancreatitis, abdominal obesity,neurodegenerative disease, retinopathy, nephropathy, Syndrome X, ovarianhyperandrogenism (polycystic ovarian syndrome), growth hormonedeficiency, neutropenia, tumor metastasis, benign prostatic hypertrophy,gingivitis, osteoporosis, and other conditions, in mammals.

The present application also provides a screening method for theidentification of agents, which bind to the secondary binding site ofdipeptidyl peptidase IV.

Further on, a screening method for the identification and determinationof one or more secondary binding sites of DP IV-like enzymes isprovided.

BACKGROUND OF THE INVENTION

The exopeptidase dipeptidyl peptidase IV (DP IV, CD26, EC 3.4.14.5) isinvolved in a number of physiological regulation processes. On the onehand, DP IV is a peptidase which can change the activity of a number ofpeptide hormones, neuropeptides and chemokines in a very specific manner(Mentlein, Reg. Pep. 85, pp. 9-24 (1999) while on the other hand the DPIV protein molecule exerts protein-protein interactions, so mediatingthe regulation of intracellular signaling cascades. A growing number ofpeptide substrates containing proline, alanine or serine in thepenultimate position are identified as substrates of DP IV in vitro andin vivo. Bioactive peptides which are substrates for DP IV and membersof such regulation cascades are, among others, NPY, GIP, GLP-1,glucagons, VIP and PACAP. Furthermore, many DP IV-inhibitors belongingto different structural classes are known.

It is known that DP IV-Inhibitors may be useful for the treatment ofimpaired glucose tolerance and diabetes mellitus (International PatentApplication, Publication Number WO 99/61431, Pederson R A et al,Diabetes. 1998 Aug; 47(8):1253-8 and Pauly R P et al, Metabolism 1999Mar; 48(3):385-9). In particular WO 99/61431 discloses DP IV-Inhibitorscomprising an amino acid residue and a thiazolidine or pyrrolidinegroup, and salts thereof, especially L-threo-isoleucyl thiazolidine,L-allo-isoleucyl thiazolidine, L-threo-isoleucyl pyrrolidine,L-allo-isoleucyl thiazolidine, L-allo-isoleucyl pyrrolidine, and saltsthereof.

Further examples of low molecular weight dipeptidyl peptidase IVinhibitors are agents such as tetrahydroisoquinolin-3-carboxamidederivatives, N-substituted 2-cyanopyroles and pyrrolidines,N-(N′-substituted glycyl)-2-cyanopyrrolidines, N-(substitutedglycyl)-thiazolidines, N-(substituted glycyl)-4-cyanothiazolidines,amino-acyl-borono-prolyl-inhibitors, cyclopropyl-fused pyrrolidines andheterocyclic compounds. Inhibitors of dipeptidyl peptidase IV aredescribed in U.S. Pat. No. 6,380,398, U.S. Pat. No. 6,011,155; U.S. Pat.No. 6,107,317; U.S. Pat. No. 6,110,949; U.S. Pat. No. 6,124,305; U.S.Pat. No. 6,172,081; WO 95/15309, WO 99/61431, WO 99/67278, WO 99/67279,DE 198 34 591, WO 97/40832, DE 196 16 486 C 2, WO 98/19998, WO 00/07617,WO 99/38501, WO 99/46272, WO 99/38501, WO 01/68603, WO 01/40180, WO01/81337, WO 01/81304, WO 01/55105, WO 02/02560 and WO 02/14271, WO02/04610, WO 02/051836, WO 02/068420, WO 02/076450; WO 02/083128, WO02/38541, WO 03/000180, WO 03/000181, WO 03/000250, WO 03/002530, WO03/002531, WO 03/002553,WO 03/002593, WO 03/004496, WO 03/004498, WO03/024965, WO 03/024942, WO 03/035067, WO 03/037327, WO 03/035057, WO03/045977, WO 03/055881, WO 03/68748, WO 03/68757, WO 03/057666, WO03057144, WO 03/040174 and WO 03/033524, the teachings of which areherein incorporated by reference in their entirety, especiallyconcerning these inhibitors, their definition, uses and theirproduction.

Definitions

The term “active site” as used in the claims and in the description isgenerally known to a person skilled in the art and means the catalyticalsite or region of DP IV and/or DP IV-like enzymes, which is responsiblefor the cleavage or biodegredation of the natural substrates of theseenzymes.

The term “secondary binding site” as used in the claims and in thedescription means a site or region of DP IV and/or DP V-like enzymes,which is different from the active site, e.g. a) a receptor site or b) asubstrate recognition site or c) a regulatory site or allosteric site.The secondary binding site can a) affect the receptor function of DP IVand/or DP IV-like enzymes or b) affect the catalytic activity of DP IVand/or DP IV-like enzymes, especially the selectivity and/or specificityof these enzymes toward their substrates. Some secondary binding sitesare complementary to the structure of the substrate of the enzymes,co-enzymes, co-factors and other compounds, which are involved in theactivity and function of the enzyme. The enzymes may even have one ormore secondary binding sites.

The secondary binding site is an element of the enzyme distinct from thecatalytic site with a different form of regulation than the competitionbetween substrates and inhibitors at the catalytic site (Darnell, J.,Lodish, H. and Baltimore, D. 1990, Molecular Cell Biology 2^(nd)Edition, Scientific American Books, New York, page 63).

The term “DP IV and/or DP IV-like enzymes” means DP IV or DP IV-likeenzymes or both.

The term “activity modifying” as used in the claims and in thedescription means both the modification of the enzymatic activity aswell as the modification of the selectivity or specificity of DP IVand/or DP IV-like enzymes. Especially preferred is the modification ofthe selectivity or specificity of DP IV and/or DP IV-like enzymes towardtheir natural substrates.

“Effectors”, as that term is used herein, are defined as molecules orligands that interact with a secondary binding site of DP IV and/or DPIV-like enzymes, thereby changing their catalytical behaviour in vitroand/or in vivo. Effectors can increase or decrease the catalyticalactivity of the enzymes. Examples of effectors are activators orinhibitors. The effectors as used herein do not act at the active sitesof enzymes, but at at least one secondary binding site, e.g. aregulatory site, or an allosteric site. The term “effectors” is usedherein synonymously with “agent” or “compound”.

The term “DP IV-inhibitor” is generally known to a person skilled in theart and means enzyme inhibitors, which interact with the active site orcatalytical site of DP IV or DP IV-like enzymes or DP IV and/or DPIV-like enzymes and inhibit the catalytical activity of these enzymes.

The “use of effectors” encompasses one single effector or two or moreeffectors together. Preferred is the use of two effectors. Especiallypreferred is the use of one single effector.

“Conditions associated with diabetes mellitus” itself includehyperglycaemia, insulin resistance, including acquired insulinresistance and obesity. Further conditions associated with diabetesmellitus itself include hypertension and cardiovascular disease,especially atherosclerosis and conditions associated with insulinresistance. Conditions associated with insulin resistance includepolycystic ovarian syndrome and steroid induced insulin resistance andgestational diabetes.

“Complications associated with diabetes mellitus” includes renaldisease, especially renal disease associated with Type 2 diabetes,neuropathy and retinopathy.

Renal diseases associated with Type 2 diabetes include nephropathy,glomerulonephritis, glomerular sclerosis, nephrotic syndrome,hypertensive nephrosclerosis and end stage renal disease.

Diabetes mellitus is preferably Type 2 diabetes.

Classification of Diabetes

Clinical diabetes may be divided into four general subclasses, including(1) type 1 (caused by beta cell destruction and characterized byabsolute insulin deficiency) (2) type 2 (characterized by insulinresistance and relative insulin deficiency (3) other specific types ofdiabetes (associated with various identifiable clinical conditions orsyndromes) and (4) gestational diabetes mellitus. In addition to theseclinical categories, two conditions—impaired glucose tolerance andimpaired fasting glucose—refer to a metabolic state intermediate betweennormal glucose homeostasis and overt diabetes. These conditionssignificantly increase the later risk of diabetes mellitus and may insome instances be part of its natural history. It should be noted thatpatients with any form of diabetes might require insulin treatment atsome point. For this reason the previously used terms insulin-dependentdiabetes (for type I diabetes mellitus) and non-insulin-dependentdiabetes (for type 2) have been eliminated.

Diabetes is currently classified as follows:

Clinical Diabetes

-   -   1. Type 1 diabetes, formerly called insulin-dependent diabetes        mellitus (IDDM) or “juvenile-onset diabetes”    -   2. Type 2 diabetes, formerly called non-insulin-dependent        diabetes (NIDDM) or “adult-onset diabetes”    -   3. Other specific types        -   a) Genetic defects of β-cell function (e.g., maturity-onset            diabetes of the young [MODY] types 1-3 and point mutations            in mitochondrial DNA)        -   b) Genetic defects in insulin action        -   c) Disease of the exocrine pancreas (e.g., pancreatitis,            trauma, pancreatectomy, neoplasia, cystic fibrosis,            hemochromatosis, fibrocalculous pancreatopathy).        -   d) Endocrinopathies (e.g. acromegaly, Cusing's syndrome,            hyperthyroidism, pheochromocytoma, glucagonoma,            somatostinoma, aldosteronoma)        -   e) Drug or chemical induced (e.g., glucocorticosteroids,            thiazides, diazoxide, pentamidine, vacor, thyroid hormone,            phenytoin [Dilantin], β-agonists, oral contraceptives)        -   f) Infections (e.g., congenital rubella, cytomegalovirus)        -   g) Uncommon forms of immune-mediated diabetes (e.g.,            “stiff-man”, syndrome, anti-insulin receptor antibodies)        -   h) Other genetic syndromes (e.g., Down, Klinefelter's,            Turner's syndrome, Huntington's disease, myotonic dystrophy,            lipodystrophy, ataxia-telangiectasia)    -   4. Gestational diabetes mellitus        Risk Categories    -   1. Impaired fasting glucose    -   2. Impaired glucose tolerance        Type 1 Diabetes Mellitus

Patients with this disorder have little or no insulin secretory capacityand depend on exogenous insulin to prevent metabolic decompensation(e.g., ketoacidosis) and death.

Commonly but not always, diabetes appears abrubtly (i.e., over days andweeks) in previously healthy non-obese children or young adults; inolder age groups it may have a more gradual onset. At the time ofinitial evaluation the typical patient often appears ill, has markedsymptoms (e.g., polyuria, polydipsia, polyhagia, and weight loss), andmay demonstrate ketoacidosis. Type 1 diabetes is believed to have a longa symptomatic p reclinical stage often lasting years, during whichpancreatic beta cells are gradually destroyed by an autoimmune attackthat is influenced by HLA and other genetic factors, as well as theenvironment. Initially, insulin therapy is essential to restoremetabolism toward normal. However, a so-called honeymoon period mayfollow and last weeks or moths, during which time smaller doses ofinsulin are required because of partial recovery of beta cell functionand reversal of insulin resistance caused by acute illness. Thereafter,insulin secretory capacity is gradually lost (over several years). Theassociation of type 1 diabetes with specific immune response (HLA) genesand the presence of antibodies to islet cells and their constituentsprovides strong support for the theory that type 1 diabetes is anautoimmune disease. This syndrome accounts for lese than 10% of diabetesin United States.

Type 2 Diabetes Mellitus

Type 2, by far the most common form of the disease, is found in over 90%of the diabetic patient population. These patients retain a significantlevel of endogenous insulin secretory capacity. However, insulin levelsare low relative to the magnitude of insulin resistance and ambientglucose levels. Type 2 patients are not dependent on insulin forimmediate survival and ketosis rarely develops, except under conditionsof great physical stress. Nevertheless, these patients may requireinsulin therapy to control hyperlgycemia. Type 2 diabetes typicallyappears after the age of 40 years, has a high rate of genetic penetranceunrelated to HLA genes, and is associated with obesity. The clinicalfeatures of type 2 diabetes may be mild (fatigue, weakness, dizziness,blurred vision, or other non-specific complaints may dominate thepicture) or may be tolerated for many years before the patient seeksmedical attention. Moreover, if the level of hyperglycemia isinsufficient to produce symptoms, the disease may become evident onlyafter complications develop.

Other Specific Types of Diabetes

This category encompasses a variety of diabetic syndromes attributed toa specific disease, drug, or condition. Genetic research has providednew insights into pathogenesis of MODY, which was formerly included as aform of type 2 diabetes. MODY encompasses several genetic defects ofbeta cell function, among which mutations at several genetic loci ondifferent chromosomes have been identified. The most common forms—MODYtype 3—is associated with a mutation for a transcription factor encodedon chromosome 12 named hepatocyte nuclear 1α (HNF 1, also known as TCF1)and—MODY type 2 is associated with mutations of the glucokinase gene (onchromosome 7) Mutations of the HNF-4α gene (on chromosome 20) areresponsible for type 1 of MODY. Each of these conditions is inherited inan autosomal dominant pattern. Two new rare forms of MODY are associatedwith mutations of the HNF-1β (on chromosome 17) and an insulin genetranscription factor termed PDX-1 or 1DX-1 (on chromosome 13).

The distinction between the various subclasses of diabetes mellitus isusually made on clinical grounds. However, a small subgroup of patientsare difficult to classify, that is, they display features common to bothtype 1 and 2 diabetes. Such patients are commonly non-obese and havereduced insulin secretory capacity that is not sufficient to make themketosis prone. Many initially respond to oral agents but, with time ,require insulin. Some appear to have a slowly evolving form of type 1diabetes, whereas others defy easy categorization.

Gestational Diabetes

The term gestational diabetes describes women with impaired glucosetolereance that appears or is first detected during pregnancy.Gestational diabetes usually appears in the 2^(nd) or 3^(rd) trimester,a time when pregnancy-associated insulin antagonistic hormones peak.After delivery, glucose tolerance generally (but not always) reverts tonormal.

Diagnosis

The diagnosis of diabetes is usually straightforward when the classicsymptoms of polyuria, polydipsia, and weight loss are present. All thatis required is a random plasma glucose measurement from venous bloodthat is 200 mg/dL or greater. If diabetes is suspected but not confirmedby a random glucose determination, the screening test of choice isovernight fasting plasma glucose level. The diagnosis is established iffasting is equal to or greater than 126 mg/dL on at least two separateoccasions.

Related Conditions

Impaired Glucose Tolerance and Impaired Fasting Glucose

Impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) areterms applied to individuals who have glucose levels that are higherthan normal, (under fed or fasting conditions, respectively) but lowerthan those accepted as diagnostic for diabetes mellitus. Both conditionsare associated with an increased risk for cardiovascular disease, but donot produce the classic symptoms or the microvascular and neuropathiccomplications associated with diabetes mellitus. In a subgroup ofpatients (about 25 to 30%), however, type 2 diabetes eventuallydevelops.

Impaired Glucose Metabolism

Impaired Glucose Metabolism (IGM) is defined by blood glucose levelsthat are above the normal range but are high enough to meet thediagnostic criteria for type 2 diabetes mellitus. The incidence of IGMvaries from country to country, but usually occurs 2-3 time morefrequently than overt diabetes. Until recently, individuals with IGMwere felt to be pre-diabetics, but data from several epidemiologicalstudies argue that subjects with IGM are heterogeneous with respect totheir risk of diabetes and their risk of cardiovascular morbidity andmortality. The data suggest that subjects with IGM , in particular,those with impaired glucose tolerance (IGT), do not always developdiabetes, but whether they are diabetic or not, they are, nonetheless,at high risk for cardiovascular morbidity and mortality. Among subjectswith IGM, about 58% have Impaired Glucose tolerance (IGT), another 29%have impaired fasting glucose (IFG), and 13% have both abnormalities(IFG/IGT). As discussed above, IGT is characterized by elevatedpost-prandial (post-meal) hyperglycemia while IFG has been defined bythe ADA (American Diabetes Association) on the basis of fasting glycemicvalues.

The categories of (a) normal glucose tolerance (NGT), (b) impairedglucose metabolism (IGM) and (c) overt type 2 diabetes mellitus areperiodically revised and adopted by the Expert Committee of the AmericanDiabetes Association (ADA). The actual values as defined in “Report ofthe Expert Committee on the Diagnosis and Classification of DiabetesMellitus. Diabetes Care (26) 1, 2003, 5-20” and “The DiabetesReady-Reference Guide for Health Care Professionals, 2000, published bythe American Diabetes Association” are:

-   -   a) Normal Glucose Tolerance (NGT)=fasting glucose level <6.1        mmol/L or less than 110 mg/dl and a 2 h post-prandial glucose        level of <7.8 mmol/L or <140 mg/dl.    -   b) Impaired Glucose Metabolism (IGM) is impaired fasting glucose        (IFG) defined as IFG=fasting glucose level of 6.1-7.0 mmol/L or        110-126 mg/dl and/or impaired glucose tolerance (IGT)=a 2 h        post-prandial glucose level (75 g OGTT) of 7.8-11.1 mmol/L or        140-200 mg/dl).    -   c) Type 2 diabetes=fasting glucose of greater than 7 mmol/L or        126 mg/dl or a 2 h post-prandial glucose level (75 g OGTT) of        greater than 11.1 mmol/L or 200 mg/dl.

These criteria were defined using the WHO recommended conditions foradministration of an oral glucose tolerance test (75 g 0 GTT) i. e., theoral administration of a glucose load containing the equivalent of 75 gof anhydrous glucose dissolved in water with a blood sample taken 2hours later to analyze to post-prandial glucose. Other OGTT testconditions have confirmed the associated risks of the IGT and IFGcategories including: 1) using 50 g glucose instead of 75 g, 2) using acasual (non-fasting) glucose sample as the analyte, and 3) analysing thepost-prandial glucose at 1 hour rather than 2 hours post-glucose load.Under all of these conditions, the glycemic categories defined abovehave been linked to the increased risks described below, but thestandardized OGTT is preferred in order to minimize variations in testresults.

Insulin resistance is not primarily due to a diminished number ofinsulin receptors but to a post-insulin receptor binding defect that isnot yet understood. This resistance to insulin responsiveness results ininsufficient insulin activation of glucose uptake, oxidation and storagein muscle and inadequate insulin repression of lipolysis in adiposetissue and of glucose production and secretion in the liver.

The term “subject” as used herein, refers to an animal, preferably amammal, most preferably a human, who has been the object of treatment,observation or experiment.

The term “therapeutically effective amount” as used herein, means thatamount of active compound or pharmaceutical agent that elicits thebiological or medicinal response in a tissue system, animal or human,being sought by a researcher, veterinarian, medical doctor or otherclinician, which includes alleviation of the symptoms of the disease ordisorder being treated.

As used herein, the term “pharmaceutically acceptable” embraces bothhuman and veterinary use: for example the term “pharmaceuticallyacceptable” embraces a veterinarily acceptable compound or a compoundacceptable in human medicine a health care.

Throughout the description and the claims the expression “acyl” candenote a C1-20 acyl residue, preferably a C1-8 acyl residue andespecially preferred a C1-4 acyl residue; “cycloalkyl” can denote aC3-12 cycloalkyl residue, preferably a C4, C5 or C6 cycloalkyl residue;and “carbocyclic” can denote a C3-12 carbocyclic residue, preferably aC4, C5 or C6 carbocyclic residue. “Heteroaryl” is defined as an arylresidue, wherein 1 to 4, and more preferably 1, 2 or 3 ring atoms arereplaced by heteroatoms like N, S or O. “Heterocyclic” is defined as acycloalkyl residue, wherein 1, 2 or 3 ring atoms are replaced byheteroatoms like N, S or O. “Peptides” are selected from dipeptides todecapeptides, preferred are dipeptides, tripeptides, tetrapeptides andpentapeptides. The amino acids for the formation of the “peptides” canbe selected from those listed above.

Throughout the description and the claims the expression “alkyl” candenote a C₁₋₅₀ alkyl group, preferably a C₆₋₃₀ alkyl group, especially aC₈₋₁₂ alkyl group; for example, an alkyl group may be a methyl, ethyl,propyl, isopropyl or butyl group. The expression “alk”, for example inthe expression “alkoxy”, and the expression “alkan”, for example in theexpression “alkanoyl”, are defined as for “alkyl”; aromatic compoundsare preferably substituted or optionally unsubstituted phenyl, benzyl,naphthyl, biphenyl or anthracene groups, which preferably have at least8 C atoms; the expression “alkenyl” can denote a C₂₋₁₀ alkenyl group,preferably a C₂₋₆ alkenyl group, which has the double bond(s) at anydesired location and may be substituted or unsubstituted; the expression“alkynyl” can denote a C₂₋₁₀ alkynyl group, preferably a C₂₋₆ alkynylgroup, which has the triple bond(s) at any desired location and may besubstituted or unsubstituted; the expression “substituted” orsubstituent can denote any desired substitution by one or more,preferably one or two, alkyl, alkenyl, alkynyl, mono- or multi-valentacyl, alkanoyl, alkoxyalkanoyl or alkoxyalkyl groups; theafore-mentioned substituents may in turn have one or more (butpreferably zero) alkyl, alkenyl, alkynyl, mono- or multi-valent acyl,alkanoyl, alkoxyalkanoyl or alkoxyalkyl groups as side groups; organicamines, amides, alcohols or acids, each having from 8 to 50 C atoms,preferably from 10 to 20 C atoms, can have the formulae (alkyl)₂N- oralkyl-NH-, —CO—N(alkyl)₂ or —CO—NH(alkyl), -alkyl-OH or -alkyl-COOH.

SUMMARY OF THE INVENTION

The inventors of the present application unexpectedly show, that thebiodegradation of different substrates, which bind to the same catalyticdomain of DP IV and/or DP IV-like enzymes, can be modulated in anunexpected very specific manner.

The invention provides a method to identify the site in the DP IVprotein or in DP IV-like enzymes or in both, DP IV and DP IV-likeenzymes which is responsible for the modulation of the substratespecificity of DP IV and also provides new compounds, which regulate thesubstrate specificity of DP IV and which are useful for the treatmentof, for example, impaired glucose tolerance, glucosuria, lipiddisorders, dyslipidemia, hyperlipidaemia, hypertriglyceridemia,hypercholesterolemia, low HDL levels, high LDL levels, metabolicacidosis, hyperglycemia, diabetes mellitus, diabetic neuropathy andnephropathy and of sequelae caused by diabetes mellitus in mammals,metabolism-related hypertension and cardiovascular sequelae caused byhypertension in mammals, for the prophylaxis or treatment of skindiseases and diseases of the mucosae, autoimmune diseases andinflammatory conditions, and for the treatment of psychosomatic,neuropsychiatric and depressive illnesses, such as anxiety, depression,sleep disorders, chronic fatigue, schizophrenia, epilepsy, nutritionaldisorders, spasm and chronic pain, atherosclerosis and its sequelae,vascular restenosis, irritable bowel syndrome, inflammatory boweldisease, including Crohn's disease and ulcerative colitis, otherinflammatory conditions, pancreatitis, abdominal obesity,neurodegenerative disease, retinopathy, nephropathy, Syndrome X, ovarianhyperandrogenism (polycystic ovarian syndrome), growth hormonedeficiency, neutropenia, tumor metastasis, benign prostatic hypertrophy,gingivitis, osteoporosis, and other conditions, in mammals.

Other Potential target diseases and the actual stage of research aresummarized in table 1. TABLE 1 Target diseases for DP IV-inhibitionTarget disease Development stage Comments AIDS cell culture mechanismnot fully understood Autoimmune cell culture and animal high dosesnecessary diseases models Rheumatoid animal models Arthritis Multiplesclerosis animal experiments Psoriasis cell culture and animalexperiments Graft rejection animal experiments Wound healing Anxietyeffective in animal models Diabetes type II Phase II studies Cancer cellculture, animal models DP IV and FAP are involved Obesity animalexperiments NPY, GLP-1 and orexine mediated

The problem of the invention is solved by using a prolyl oligopeptidase(POP) based computer-generated model of DP IV and of the crystalstructure of DP IV for the identification of secondary binding sites ofDP IV and by providing specific compounds, which bind to at least onesecondary binding site and are able to modify very differently and/orspecifically the DP IV-catalyzed truncation of substrates of DP IV andDP IV-like enzymes, e.g. bioactive peptides. The overall result is asignificant increase of substrate dependent DP IV-selectivity by suchcompounds and thereby minimization of side reactions with othersubstrates and as such of potential side effects after completeinhibition of DP IV-activity.

BRIEF DESCRIPTION OF THE DRAWINGS

Further understanding of these and other aspects of the instantinvention may be had by reference to the figures wherein:

FIG. 1 shows a plot of the distribution of the backbone dihedral anglesof the complete model of human DP IV. There are no residues indisallowed regions, but some residues are located in only generouslyallowed areas. Most of them represent residues in loops at the surfaceof the propeller domain.

The plot statistics is a measure for the plot quality. The plotstatistics for FIG. 1 is as follows: Residues in most favoured regions435 62.8% Residues in additionally allowed regions 226 32.6% Residues ingenerously allowed regions 32 4.6% Residues in disallowed regions 0 0.0%Number of non-glycine and non-proline residues 693 100.0% Number ofend-residues (excl. Gly and Pro) 1 Number of glycine residues (shown astriangles) 43 Number of proline residues 29 Total number of residues 766

FIG. 2 shows the analysis of the quality of the model of human DP IVwith regard to some essential stereo-chemical parameters. The plotstatistics is as follows: No. of Comparison band Values widthsStereochemical No. of Parameter Typical Band from parameter data pointsvalue value width mean a. %-tage residues in 693 63.9 83.8 10.0 −2.0WORSE A, B, L b. Omega angle 765 4.7 6.0 3.0 −0.4 Inside standarddeviation c. Bad contacts/100 19 2.5 4.2 10.0 −0.2 Inside residues d.Zeta angle standard 723 3.5 3.1 1.6 0.3 Inside deviation e. H-bondenergy 389 0.9 0.8 0.2 0.5 Inside standard deviation f. Overall G-factor766 −0.6 −0.4 0.3 −0.5 Inside

FIG. 3 shows the computer-assisted structure model of DP IV and theADA-binding site (indicated by the arrows and amino acid residuenumbers);

FIG. 4 shows the active site of DP IV docked with the active site DPIV-inhibitor isoleucyl pyrrolidine (Ile-Pyr) (dark gray);

FIG. 5 shows the interaction of Lys-Z-nitro-pyrrolidine with the activesite of DP IV;

FIG. 6 shows the tetrahedral intermediate of Asp-Pro-pNA bound to DP IV;

FIG. 7 shows the interaction of the HIV-tat(1-9) protein with DP IV;

FIG. 8 shows the docking of the N-terminal nonapeptide of the tromboxanereceptor;

FIG. 9 shows the 3D-structure model of the interaction between GIP(black thread) and human DP IV;

FIG. 10 shows the docking arrangement of GIP (black) to the active siteof DP IV;

FIG. 11 shows the molecular dynamic simulation based model of thetertiary structure of GIP (middle part), bound to DP IV. Important aminoacid residues from the enzyme are shown in light gray, those from GIPare shown in black, respectively;

FIG. 12 shows the docking of VIP (black) to the active site of DP IV;

FIG. 13 shows the docking of the C-terminal part of VIP to DP IV;

FIG. 14 shows the docking of glucagon (black) to the active site of DPIV;

FIG. 15 shows the molecular dynamic simulation based model of thehexapeptide TFTSDY, bound to the secondary binding site of DP IV.Important amino acid residues from the enzyme are light gray, those fromthe hexapeptide are marked in dark gray, respectively;

FIG. 16 shows the prolongation of the half-lifes of GIP, Glucagon,PACAP-27 and PACAP-38 by the hexapeptide TFTSDY in a DP IV (porcine andrecombinant human) catalyzed peptide truncation test;

FIG. 17 shows the DP IV-catalyzed hydrolysis of RANTES1-15 with (blacksolid triangle or broken line) or without TFTSDY (black solid square orstraight line);

FIG. 18 shows the DP IV-catalyzed hydrolysis of GIP with (black solidtriangle) or without TFTSDY (black solid square);

FIG. 19 shows the DP IV-catalyzed hydrolysis of glucagon with (blacksolid circle) or without TFTSDY (black solid triangle);

FIG. 20 shows a plot of the distribution of the backbone dihedral anglesof the complete model of porcine DP IV. All residues are in most favoredand additional allowed regions. The plot statistics is as follows:Residues in most favoured regions (A, B, L) 457 66.0% Residues inadditional allowed regions (a, b, l, p) 235 34.0% Residues in generouslyallowed regions (˜a, ˜b, ˜l, ˜p) 0 0.0% Residues in disallowed regions 00.0% Number of non-glycine and non-proline residues 692 100.0% Number ofend-residues (excl. Gly and Pro) 2 Number of glycine residues (shown astriangles) 44 Number of proline residues 31 Total number of residues 769

FIG. 21 shows the analysis of the quality of the model of porcine DP IVwith regard to some essential stereo-chemical parameters of the mainchain. The plot statistics is as follows: No. of Comparison band No. ofValues widths data Parameter Typical Band from Stereochemical parameterpoints value value width mean a. %-tage residues in A, B, L 692 66.083.8 10.0 −1.8 WORSE b. Omega angle standard 765 8.5 6.0 3.0 0.8 Insidedeviation c. Bad contacts/100 residues 2 0.3 4.2 10.0 −0.4 Inside d.Zeta angle standard deviation 725 2.1 3.1 1.6 −0.6 Inside e. H-bondenergy standard 400 0.8 0.8 0.2 −0.1 Inside deviation f. OverallG-factor 769 −0.4 −0.4 0.3 −0.1 Inside

FIG. 22 shows the analysis of the quality of the model of porcine DP IVwith regard to some essential stereo-chemical parameters of the sidechains. The plot statistics is as follows: No. of band No. of ComparisonValues widths data Parameter Typical from Stereochemical parameterpoints value value Band width mean a. Chi-1 gauche minus 156 16.2 18.16.5 −0.3 Inside standard deviation b. Chi-1 trans standard 218 17.9 19.05.3 −0.2 Inside deviation c. Chi-1 gauche plus standard 279 17.6 17.54.9 0.0 Inside deviation d. Chi-1 pooled standard 653 18.0 18.2 4.8 0.0Inside deviation e. Chi-2 trans standard 144 16.3 20.4 5.0 −0.8 Insidedeviation

FIG. 23 shows soluble DP IV from prorcine kidney, which forms a 2-2-2symmetric assembly as dimer of dimers. The view is along one two-foldaxis. Potential glycosylation sites are indicated as grey spheres, blackspheres are the sites modified in the crystal structure. Thetransmembrane helices and their orientation to the membrane were modeledto illustrate how tetramerization of DP IV can mediate cell-cellcontacts. The figure was prepared by using the program MOLSCRIPT andRASTER3D.

FIG. 24 shows a topology diagram illustrating the domain structure ofporcine kidney DP IV. Blade IV of the propeller is involved in both thedimer contact (IV A-IV B: L235-P255, together with the highlightedC-terminal three secondary structure elements F713-C762) and thetetramerization of DP IV (IV A-IV C and IV B-IV C, not shown).

FIG. 25 shows oligomerization interfaces. (A) Detailed viewperpendicular to the dimer two-fold axis. The experimental electrondensity after phase extension to 2.0 Å resolution is superimposed on keyresidues mediating the contact. (B) View along the two-fold axis on thetetramerization interface. Blades IV of each subunit align to form aneight-bladed antiparallel β sheet. The highlighted Leu294 and Val341 areinvolved in ADA binding. The figure was prepared using BOBSCRIPT,MOLSCRIPT and RASTER3D.

FIG. 26 shows substrate recognition by procine kidney DP IV. (A) Thepeptidomimetic active-site inhibitor p-Iodo-Phe-Pyr-CN is bound toactive site. The accessible surface is indicated and cut-open (dark grayarea at the top of the figure) for better visibility. (B) Schematicrepresentation of the active site access in tricom and DP IV. The figurewas prepared by using the programs MAIN , MOLSCRIPT, GRASP and RASTER3D.

FIG. 27 shows the DP IV-catalyzed hydrolysis of GIP₁₋₄₂ with (blacksolid squares) or without the heptapeptideH-Ser-D-Glu-Thr-Gly-D-Val-D-Lys-D-Val-OH (black solid triangles).

DETAILED DESCRIPTION OF THE INVENTION

The inventors of the present application unexpectedly show, that thebiodegradation of substrates, which bind to the same catalytic domain ofDP IV, can be modulated very specifically.

One aspect of the invention is to identify the site in the DP IVprotein, which is responsible for the modulation of the substratespecificity and selectivity of DP IV and DP IV-like enzymes and toprovide new compounds, which regulate the substrate selectivity and/oractivity of DP IV and DP IV-like enzymes and which are useful for thetreatment of, for example, impaired glucose tolerance, glucosuria, lipiddisorders, dyslipidemia, hyperlipidaemia, hypertriglyceridemia,hypercholesterolemia, low HDL levels, high LDL levels, metabolicacidosis, hyperglycemia, diabetes mellitus, diabetic neuropathy andnephropathy and of sequelae caused by diabetes mellitus in mammals,metabolism-related hypertension and cardiovascular sequelae caused byhypertension in mammals, for the prophylaxis or treatment of skindiseases and diseases of the mucosae, autoimmune diseases andinflammatory conditions, and for the treatment of psychosomatic,neuropsychiatric and depressive illnesses, such as anxiety, depression,sleep disorders, chronic fatigue, schizophrenia, epilepsy, nutritionaldisorders, spasm and chronic pain, atherosclerosis and its sequelae,vascular restenosis, irritable bowel syndrome, inflammatory boweldisease, including Crohn's disease and ulcerative colitis, otherinflammatory conditions, pancreatitis, abdominal obesity,neurodegenerative disease, retinopathy, nephropathy, Syndrome X, ovarianhyperandrogenism (polycystic ovarian syndrome), growth hormonedeficiency, neutropenia, tumor metastasis, benign prostatic hypertrophy,gingivitis, osteoporosis, and other conditions.

Usually, DP IV is inhibited by compounds mimicking the N-terminaldipeptide part of a DP IV-substrate. This leads to potent compoundswhich are inhibitors of DP IV and DP IV-like enzymes and inhibit atsufficient concentrations (e.g. 5× K_(i)-dose) the DP IV-catalyzedhydrolysis of small chromogenic or higher molecular weight peptidesubstrates. In the present invention it is demonstrated that compoundsinteracting with DP IV-binding sites far distant from the catalyticcenter are capable to differentiate the degradation of differentsubstrates, e.g. peptide substrates, or even discriminate DPIV-catalyzed hydrolysis completely.

The substrate properties of the peptides of the growth hormone releasingfactor (GRF) family against DP IV were examined.

The GRF family consists of the following peptide hormones:

-   -   Gastrin-releasing peptide (GRP)    -   Enterostatin    -   Peptide histidine methionine (PHM)    -   Cholecystokinin    -   Glucagon-like peptide-2 (GLP-2)    -   Glucose-dependent insulinotropic polypeptide (GIP)    -   Glucagon-like peptide-1 (GLP-1)    -   Growth-hormone releasing factor (GRF)    -   Pituitary-adenylate cyclase activating polypeptide (PACAP (27        und 38))    -   Vasoactive intestinale peptide (VIP)    -   Exendin-1    -   Exendin-2    -   Exendin-3    -   Exendin-4    -   Secretin    -   Glucagon

In particular, the capability of purified DP IV from human, from porcinekidney, of recombinant human DP IV and the DP IV activity of the humanserum to truncate the peptides of the GRF family were analyzed. Thehalf-life of the peptides were determined using matrix-assisted laserdesorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS)whereas the kinetic constants K_(m) and k_(cat)/K_(m) were calculatedusing capillary zone electrophoresis. All peptides were hydrolyzed byporcine DP IV, recombinant human DP IV or DP IV activity of the humanserum. The resulting K_(m)-values were independent from the amino acidin the P₁-position. That means that the binding of substrates to DP IVis not mainly affected by the P₁-residue rather than by secondaryinteractions between substrate and DP IV protein.

The same surprising phenomenon of different substrate properties wasshown with GIP-fragments of different chain lengths. V²GIP( 1-6) andG²GIP( 1-6) were not hydrolyzed by DP IV. V²GIP(1-30) and G²GIP(1-30)were accepted as substrates and both S²GIP(1-6) and S²GIP(1-30) weretruncated by DP IV (Table 2). These findings prove the existence of asecondary binding site in the DP IV protein, which is responsible forsubstrate recognition and which modulates the biodegradation ofsubstrates and, therefore forms the basis for the management ofsubstrate selectivity and specificity of DP IV and/or DP IV-likeenzymes. TABLE 2 Truncation half life of various bioactive peptideswhich are substrates for DP IV substance half-life [min] GIP₁₋₃₀ 2.68S²GIP₁₋₃₀ 137.14 V²GIP₁₋₃₀ 298.04 G²GIP₁₋₃₀ 150.02 GIP₁₋₆ <7.5 S²GIP₁₋₆79.04 V²GIP₁₋₆ no degradation G²GIP₁₋₆ no degradation

The amino acid sequences of natural GIP₁₋₃₀ and GIP₁₋₆ are: GIP_(1-30:)YAEGTFISDYSIAMAKIHQQAFVNWLLAQK GIP_(1-6:) YAEGTF

To identify the secondary binding site, a hexapeptide derived from aconsensus sequence of the amino acid sequences of GRF-family peptideswas synthesized and its influence on the substrate specificity of DP IVwas measured. The selected consensus sequence corresponds toglucagon₅₋₁₀, comprising the amino acid sequence TFTSDY. As expectedthis peptide had only weak influence on the GP-4-Nitroanilide hydrolysis(K_(i)=0.71 mM).

In support of the results achieved with the GRF family peptides, thetruncation half-lifes of GIP, GLP-1, NPY, glucagon or PACAP by DP IVwere also changed after preincubation with 160 μM TFTSDY (Table 3). Nodifferences could be detected between incubation of Rantes₁₋₁₅ and DP IVwith or without the hexapeptide TFTSDY (Table 3). The latter findingshows that the peptide Rantes₁₋₁₅ is too short to reach the secondarybinding site and therefore TFTSDY has no effect on its hydrolysis rate.The half-lives of GIP and glucagon in presence of DP IV were prolongedby TFTSDY, the strongest influence had TFTSDY on the DP IV-catalyzedtruncation of glucagon.

Further, a modified variant of the hexapeptide TFTSDY, TFTDDY wassynthesized, studied for docking in the DP IV 3D structural model andtested for its regulatory efficacy to modulate substrate specificity ofDP IV. TABLE 1 Inhibitory effect of TFTSDY on DP IV-catalyzed peptidetruncation expressed in K_(i)-values K_(i) [μM] peptide rec. human DP IVporcine DP IV PACAP-27 26.7 n.d. PACAP-38 2.8 n.d. GIP 14.0 65.9glucagon 3.7 6.8 RANTES₁₋₁₅ n.d. 12307.7 GLP-1 n.d. 13.7 NPY n.d. 17.2n.d.—not determined

The hexapeptides TFTSDY and TFTDDY were found to be instable inbiological fluids, e.g. humen serum or human plasma and/or they wererapidly degraded by proteolytic enzymes in the serum or plasma.Therefore, and in another embodiment of the present invention, aheptapeptide of the sequence H-Ser-D-Glu-Thr-Gly-D-Val-D-Lys-D-Val-OHwas synthesized. This heptapeptide is not enzymatically degraded inhuman serum or plasma and is stable in these fluids. A stabilization ofthe heptapeptide was especially achieved by the incorporation of D-aminoacids in the molecule. It was further shown to be very effective inimproving the substrate specificity of DP IV compared to controlexperiments without the heptapeptide.

The existence of a secondary binding site was proven, e.g. using a setof dipeptide compounds, coupled to a chromogenic (p-nitroaniline, pNA)or fluorogenic (aminomethylcoumarine, AMC) group. The dipeptidesHis-Pro, His-Ala, His-Ser, His-Val, His-Gly, and His-Thr represent thefirst two amino acids from the N-terminus of the following peptidehormones: GIP, GLP-1, GLP-2, PACAP, VIP, PHM and glucagon. The peptidehormones GIP, GLP-1, GLP-2, PACAP, VIP, PHM and glucagon are substratesof DP IV. DP IV hydrolizes these peptide hormones and the respectiveN-terminal dipeptides are released. In contrast, the dipeptides are muchslower released, when they are coupled to the chromogenic(p-nitroaniline, pNA) or fluorogenic (aminomethylcoumarine, AMC) group.Secondary interactions of the peptide hormones GIP, GLP-1, GLP-2, PACAP,VIP, PHM and glucagon far from the DP IV active site must exist as aprerequisite for substrate recognition. Data supporting the existence ofa secondary binding site of DP IV are shown in table 4 below TABLE 4 DPIV-catalyzed hydrolysis of His-Ser-, His-Gly and His-Val-dipeptidescompared to the full-lenght substrates glucagon and NPY. Compound K_(m)[M] His-Ser-AMC 2.1 * 10⁻² Glucagon 3.8 * 10⁻⁶ His¹-Ser²-NPY 6.8 * 10⁻⁵His-Gly-AMC 4.1 * 10⁻⁴ [Gly]²-glucagon 2.2 * 10⁻⁵ His-Val-AMC 1.9 * 10⁻²The Prolyl Oligopeptidase (POP) Based Computer-Generated Models of HumanDP IV

Prolyl oligopeptidase (POP) based computer-generated models of human DPIV and porcine DP IV and the crystal structure of porcine DP IV wereused according to the present invention to predictenzyme-substrate-interactions and to identify the interaction site inthe DP IV protein structure.

Since the sequence homology between DP IV and the template POP is notvery high, standard methods for homology modeling such as theapplication of COMPOSER gave only very crude preliminary models whichneeded a lot of manual modification and improvements. These improvementswere made by inspection of the conformation and spatial position of eachof the 766 amino acid residues with regard to forming sheets or helicesand favored intra-residual interactions such as hydrogen bonds, saltbridges and hydrophobic interactions as well. All modifications madewere examined by using PROCHECK, which allows the analysis of thestereochemical quality of the model (dihedral angles in favored areas ofa Ramachandran Plot, see FIG. 1 for human DP IV and FIG. 20 for porcineDP IV), bond angles and bond length, hydrogen bonds (see FIG. 2 forhuman DP IV and FIGS. 21 and 22 for porcine DP IV), and by PROSA whichanalyzes its energy in comparison to native folded proteins. All theseresidues show that some residues are located in unfavorable areas butall belong to loop regions of the propeller domain which is not ofessential importance for docking studies and predictions of new ligands.

In summary of this part, the model of DP IV used herein is in a statewhere the overall fold is correct and highly useful for the explanationof experimental results and to allow predictions of recommendations forpositions of site directed mutagenesis, development of ligands based onthe identified second binding site or selective ligands to bind at thecloser active site.

In order to identify essential amino acids for the secondary interactionindependently from the active site, site-directed mutageneses wereperformed using human DP IV cDNA. The mutation sites were: W629A andR560A. The characterization of these mutants showed that both mutationshave no influence on the enzyme catalyzed hydrolysis ofGP-4-nitroanilide and the kinetic parameters of short and/or lowmolecular weight inhibitors, which are directed to the active site of DPIV (see table 5). Another mutated enzyme variant, R310A, was expressedas inactive protein. This mutation resulted in the appearance of threeDP IV fragments. Based on the computer generated model was shown that anintramolecular salt bridge is formed between R310 and D332 and that thisintramolecular salt bridge is crucial for the formation andstabilization of the DP V tertiary protein structure. TABLE 5 Kineticcharacterization of DP IV-catalyzed substrate hydrolysis by mutants ofDP IV in the secondary binding site Test K_(m) K_(i) kcat k_(cat)/K_(m)Mutation compound [M] [M] [s⁻¹] [M⁻¹ * s⁻¹] mu 15 DP IV Gly-Ser-AMC Nothydrolyzed mu 15 DP IV Gly-Pro-AMC 4.66E−05 1.00E+06 2.15E+10 mu 15 DPIV V²GIP(1-4)* no inhibition mu 15 DP IV S²GIP(1-6)* no inhibition mu 15DP IV Glucagon (1-14)* no inhibition mu 15 DP IV Leu-hia-Fum* 6.81E−08mu 15 DP IV TFTSDY* no inhibition mu 15 DP IV PACAP(1-38)* 3.67E−05 mu15 DP IV Transp 01* 7.69E−08 mu 15 DP IV YAESTF amide* 1.14E−06 mu 16 DPIV Gly-Ser-AMC Not hydrolyzed mu 16 DP IV Gly-Pro-AMC 5.02E−05 1.44E+062.86E+10 mu 16 DP IV V²GIP(1-4)* no inhibition mu 16 DP IV S²GIP(1-6)*no inhibition mu 16 DP IV Glucagon (1-14)* no inhibition mu 16 DP IVPACAP(1-38)* 3.21E−05 mu 16 DP IV Transp 01* 8.55E−08 mu 16 DP IV YAESTFamide* 1.06E−06 mu 16 DP IV TFTSDY* no inhibition mu 16 DP IV Leu-ThiaFum* 6.57E−08 rh wt DP IV Gly-Ser-AMC  4.4E−04 rh wt DP IV Gly-Pro-AMC3.53E−05 1.66E+06 4.7E+10 rh wt DP IV V²GIP(1-4)* no inhibition rh wt DPIV S²GIP(1-6)* no inhibition rh wt DP IV Glucagon (1-14)* no inhibitionrh wt DP IV PACAP(1-27)* 2.28E−04 1.13E−04 rh wt DP IV PACAP(1-38)*3.83E−05 rh wt DP IV Transp 01* 5.08E−08 rh wt DP IV YAESTF amide*3.51E−08 rh wt DP IV TFTSDY* no inhibition rh wt DP IV Leu-Thia Fum*4.26E−05 6.58E−08 p wt DP IV Leu-Thia-Fum* 5.98E−05 7.29E−08 p wt DP IVPACAP(1-27)* 1.22E−04 5.43E−05*The Ki-values were determined in competition of the test compound tothe standard substrate GP-4NA (see examples). No inhibition means thatthe compound doesn't influence the DP IV-catalyzed hydrolysis of thestandard substrate GP-4NA.

Definitions in table 5: mu 15 recombinant human DP IV, mutation R560A mu16 recombinant human DP IV, mutation W629A rh wt recombinant human DPIV, wild type p wt porcine kidney DP IV, wild type Transp 01RRLSYSRRRF-E-Thia

In the present invention a region was identified in the DP IV-protein,which is responsible for the interaction with a hexapeptide, e.g. TFTSDYor TFTDDY, or more suitably, a degadation resistent heptapeptide, e.g.H-Ser-D-Glu-Thr-Gly-D-Val-D-Lys-D-Val-OH. The most important amino acidsfor the formation of the secondary binding site on DP IV for the GRFfamily of peptide hormones were found to be but are not restricted toL90, E 91, T 152, W154, W157, R310, Y330, R318, Y416, S460, K463, E464and R560.

The Cyrstal Structure of DP IV

In a further embodiment of the present invention, the sequence and 1.8 Åcrystal structure of native DP IV prepared from porcine kidney weredetermined. The crystal structure reveals a 2-2-2 symmetric tetramericassembly which depends on the natively glycosylated β-propeller bladeIV. The crystal structure indicates that tetramerization of DP IV is akey mechanism to regulate its interaction with other components. Eachsubunit comprises two structural domains, the N-terminal eight-bladedβ-propeller with open Velcro topology and the C-terminal α/β-hydrolasedomain. Analogy with the structurally related POP and tricom proteasesuggests that substrates access the buried active site through theβ-propeller tunnel while products leave the active site through aseparate side exit. A dipeptide mimicking inhibitor complexed to theactive site discloses key determinants for substrate recognition,including a Glu-Glu motif which distinguishes DP IV as an aminopeptidaseand an oxyanion trap which binds and activates the P₂-carbonyl oxygennecessary for efficient post-proline cleavage.

Sequence of the Porcine DP IV

Sequence comparison of the porcine DP IV with the human and othermammalian DP IV-sequences reveals a very high degree of sequenceconservation. In particular, there is not a single sequence insertion ordeletion between the porcine and the human sequence. The overallsequence identity between these two species is 88%. (and 92% within thecatalytic domain). Noteworthy, Ser339 in the porcine sequencesubstitutes for Cys339 in the human sequence, causing the absence of anextra disulfide bond (Cys328-Cys339) in human DP IV. In comparison tothe human sequence the potential glycosylation site at Asn520 is lostbecause of an Asn-His exchange. On the other hand there is an additionalpotential glycosylation site at Asn179 which is not found in the humansequence. Interestingly, the glycosylation site at Asn279 is found atAsn281 in the human sequence.

Recently, the structure of human DP IV was published (PDB entry code1N1M) (Rasmussen H. B., Branner, S., Wiberg, F. C., Wagtmann, N. (2002)http://www.nature.com/naturestructuralbiology, published online 16 Dec.2002.) The model of porcine DP IV according to the present invention wasrefined by using the program CNS with current R-values of 21.7% (workingset) and 24.9% (test set) and deviations from ideality of 0.008 Å (bondlength) and 1.4 degree (angle deviation).

Overall Structure and Subunit Assembly

The monomer comprises an N-terminal β-propeller domain (Arg54-Asn497)followed by the catalytic domain Gln508-Pro766. Notably, the crystalstructure reveals a dimer of DP IV dimers in the crystallographic unitcell obeying a 222 symmetry with all axes intersecting, FIG. 23. The byfar more extensive dimer contact is predominantly mediated by residuesof the catalytic domain with a contact area of 2270 Å² versus thedimer-to-tetramer interface of 2×570 Å²=1140 Å². The dimer interface isdominated by hydrophobic interactions, with a central and well shieldedaromatic stacking involving Trp734 and Phe713 of both monomers. Thehydrophobic contacts are complemented by polar interactions such asAsp729 with His754 and His757, FIG. 25A. Notably, theGln731(Oε1)-Gln731(Nε2) contact resembles a subtle (atomic) break of theexact two-fold symmetry within the dimer. The residues critical to thedimerization are strictly conserved throughout all species.

The dimer-dimer interface has a more hydrophilic character. In itscenter, the strands Asn279-Gln286 of each DP IV-dimer form anantiparallel β-sheet, thus extending propeller blade IV to aneight-stranded antiparallel sheet, FIG. 25B. An additional contributionto the tetrameric assembly in our crystals arises from the outer strandsof blade V. The residues contributing to the dimer-dimer contact aresimilar over different species, albeit especially in rodents notstrictly identical. More importantly, there are no insertions ordeletions in the outer β strands of blade IV with a contact area of 570Å² per monomer. Significantly, Asn279 is located at the tetramerizationinterface and is glycosylated (FIGS. 23, 25B). Thus, glycosylation ofAsn279 might provide one missing regulatory link which was proposed tocontrol the assembly of a 900 kDa oligomer (Lambeir, A. M., Pereira, J.F. D., Chacon, P., Vermeulen, G., Heremans, K., Devreese, B.,VanBeeumen, J., Demeester, I. & Scharpe, S. (1997) Biochim. Biophys.Acta 1340, 215-226.).

Subdomain Structure

The β-propeller. The N-terminal β-propeller domain contains eight bladeswith four antiparallel strands each. Typically for β propellerstructures, the first and the last blade of a β-propeller is clampedtogether either covalently by disulfide bond formation (four-bladedβ-propellers) or by strand exchange between the first and last blade(five to eight-bladed propellers). So far there are three exceptions tothis closed propeller topology rule, namely the seven bladed β-propellerof POP (Fülöp, V., Bocskei, Z. & Polgár, L. (1998) Cell 94, 161-170.),the seven and the six bladed propellers of the tricom protease(Brandstetter, H., Kim, J. -S., Groll, M. & Huber, R. (2001) Nature 414,466-469.), and the five bladed propeller of α-L-arabinase 43A (Nurizzo,D., Turkenburg, J. P., Charnock, S. J., Roberts, S. M., Dodson, E. J.,McKie, V. A., Taylor, E. J., Gilbert, H. J. & Davies, G. J. (2002)Nature Struct. Biol. 9, 665-668.). The β8-propeller of DP IV can also beclassified as an open Velcro-type topology, because no segmentC-terminal to blade VIII interacts with the first propeller blade.Interestingly, however, the interaction of the first strand within bladeI is limited to Thr59-Ile63 while its N-terminal extension Phe53-Tyr58tightens up the propeller structure by interacting with the immediateC-terminal extension to the fourth strand of blade VIII (Glu499-Met503).A similar, yet shorter, external clamp has been described for theδ7-propeller of the tricorn protease (Brandstetter, H., Kim, J. -S.,Groll, M. & Huber, R. (2001) Nature 414, 466-469.).

With the exception of Cys649-Cys762 all disulfide bonds are located inthe β propeller domain where they form intra-blade stabilizingcrosslinks exclusively, FIG. 24. Cys339 in the human sequence isreplaced by Ser339 in the porcine sequence which causes the absence ofthe disulfide bond connecting strand 3 and 4 of blade V (Cys328-Cys339in human DP IV), although the backbone conformation of the strands wouldreadily allow a disulfide bond to be formed. Similarly, allglycosylation sites but Asn685 are located on the β-propeller. Five ofin total 10 potential glycosylation sites cluster at the top surfaceside oriented away from the catalytic domain. Four are positioned on theloops connecting strand 3 and 4 of blade I (Asn85), III (Asn179), IV(Asn279) and VI (Asn393), one on the loop connecting strand 1 and 2 ofblade IV (Asn219), FIGS. 23, 24. Intriguingly, out of these fivepotential glycosylation sites only Asn279 is actuallyposttranslationally modified which is involved in the tetramerization ofDP IV. Further glycosylation sites are located on blade I (Asn92 at theend of strand 4), blade IV (Asn229 close to the tetramerization motif),blade V (Asn321 on the loop connecting strand 2 and 3), FIG. 23, 24.Asn150 on the exit strand of blade II is not actually modified in thecrystals. The shape of the DP IV-β8-propeller is asymmetric where bladesVI, VII, VIII, I, and blades II, III, IV, V form more compactsubdomains, respectively (FIGS. 23, 25B). The structural division of theβ-propeller fits physico-chemical data which indicated a three domainorganization of DP IV (Lambeir, A. M., Pereira, J. F. D., Chacon, P.,Vermeulen, G., Heremans, K., Devreese, B., VanBeeumen, J., Demeester, I.& Scharpe, S. (1997) Biochim. Biophys. Acta 1340, 215-226.). Theellipsoidal tunnel through the propeller is continuously open. At thesolvent exposed opening, its diameter measures 9 Å and 15 Å from bladeIV to VIII and from blade II to VI, respectively. The tunnel widenstowards the catalytic domain with opening diameters of 15 Å and 25 Åbetween the same pairs of propeller blades. By its dimensions, thetunnel allows for direct passage of an extended peptide, but not for afolded α-helix.

Only few solvent molecules are visible in the tunnel, most remarkable asulfate is bound to the oxyanion pocket formed by the amide nitrogens ofGlu361 and Ile407 and Nε2 of His363.

The Catalytic domain. The catalytic domain is located at the C-terminusof DP IV and spans residues Gln509 to Pro766. It adopts a typicalα/β-hydrolase fold with a central 8 stranded β sheet, where only thesecond strand Thr522-Pro531 deviates from the otherwise parallel strandpolarity, FIG. 23. The β-sheet exerts a significant twist of more than90 degrees, in line with observations on related α/β-hydrolases.

Within the catalytic domain a single disulfide bond Cys649-Cys762crosslinks the C-terminal helix Met746-Ser764 with the sixth strand ofthe β-sheet (Lys648-Ala654), thus stabilizing its tertiary arrangement.Helix Met746-Ser764, together with helix Gln714-Asp725 and strandAsp729-Thr736 from the C-terminal region, constitutes the centraldimerization motif which is further stabilized through an interactioncontributed by the oligomerization blade IV of the β-propeller.

The β-sheet is sandwiched by several a-helices, including helixTyr631-Ala642 immediately succeeding the catalytic Ser630. Ser630 isembedded in the surrounding secondary structure framework where itparticipates both in the preceding strand 4 (Arg623-Trp629) as well asin the following helix Tyr631-Ala642. This causes a strained backboneconformation of the active site Ser630. The high energy conformation ofSer630 is reflected by its dihedral angles (Φ, ψ)=(61.4,-115.7) andpresumably provides a reservoir needed for catalysis (Goettig, P.,Groll, M., Kim, J. -S., Huber, R. & Brandstetter, H. (2002) EMBO J 21,5343-5352.).

Active site and substrate recognition. The sequential andthree-dimensional arrangement of the catalytic residues Ser630, His740,Asp708 corresponds to that of related α/β-hydrolases. The oxyanion holeis formed by the amide Tyr631 and the hydroxyl Oη of Tyr547 and servesto recognize and activate the carbonyl oxygen of the P₁-residue. It isoccupied by a water molecule in the uninhibited structure. To detail theexact mechanism of substrate recognition, the structure of a dipeptidmimetic, the iodinated Phe-cyanopyrrolidide inhibitor in complex with DPIV was determined (FIG. 26A). The active site nucleophile, the hydoxylresidue of Ser630, forms a covalent bond with the scissile carbonylcarbon of the cyanopyrrolidine of the inhibitor. The bending of thelinkage (FIG. 26A) indicates the formation of a stable carbaminic acidadduct. The pyrrolidine ring is accommodated by a hydrophobic pocketformed by side chains of Tyr666, Tyr662, Val711, Val656 and Trp659.While this environment is almost perfectly suited for the imino acidproline as P₁-residue, the hydroxyl Oη of Tyr662 would be correctlypositioned to interact with the normal amide nitrogen of an amino acidin P₁. The inhibitor also unambiguously maps the S₂-site. TheP₂-carbonyl oxygen gets trapped in an electrostatic sink formed by theside chains of Arg125 and Asn710. Glu205 and Glu206, and to a lesserextent the carbonyl oxygen of Glu205, interact with the free aminoterminus of the P₂-residue, thus determining the dipeptidyl“amino”-peptidase activity of the enzyme. It is, therefore, theβ-propeller which provides essential determinants for P₂-recognition,namely Arg125, which is positioned on the hairpin loop between strands 2and 3 of blade II and Glu205-Glu206, positioned on a short helicalinsertion within strand 1 of the β propeller blade IV. Ample space isavailable to accommodate voluminous side chains such as Tyr or Trp inP₂, FIG. 26A. In our inhibitor the phenyl ring of the P₂-residue isiodated rather than hydroxylated. It forms an ionic interaction withArg358, FIG. 26A.

Substrate access to and product egress from the active site. Theβ-propeller domain covers the active site and thereby restricts thesubstrate access to it. There are two possible routes to the activesite, namely through the tunnel of the β-propeller and through a sideopening. Similar as the propeller tunnel, the shape of the side entranceis oval with dimensions of 15 Å and 22 Å. The side opening to the activesite is generated by the kinked blade arrangement of blade I and II,FIG. 23. In POP, blades I and II are arranged more regularly and thereis no side opening to the active site chamber. The distance from theprotein surface to the active site measures 20 Å and 37 Å through theside opening and the propeller tunnel, respectively. From itsdimensions, both routes give active site access to unfolded peptidicsubstrates, but the side entrance is significantly shorter and lesswinded. Once the substrate has been cleaved, two products have to leavethe active site chamber. Clearly, the product exit route differs fromthe entrance to the active site.

Based on the crystal structure model new functional characteristics ofDP IV were identified and are part of the present invention. These newfeatures of DP IV are:

Oligomerization of membrane-bound and soluble DP IV. Tetramerization onthe cell surface involves, for geometric reasons, a membrane bound and asoluble DP IV dimer pair or dimers located on the surface of twodifferent cells, as illustrated on FIG. 23. DP IV is known as acell-cell communication molecule. Thus, the way DP IV is involved inmediating such cell-cell contacts may be by tetramerization of twohomodimers present on the surface of interacting cells. Alternatively,soluble dimers can assemble to form a homotetramer, as observed in thecrystal structure described above. The tetramer assembles to enclose alarge cavity. Since tetramerization of DP IV depends on the correctlyglycosylated propeller blade IV, glycosylation could function as aquality control unit.

Dimerization is mediated by the three C-terminal secondary structureelements positioned on the catalytic domain, and a finger like insertionmotif within strand 2 and 3 of propeller blade IV. Furthermore, DP IV isknown to form heterodimers with fibroblast activation protein α (FAPα,seprase). Like DP IV (FAPβ), FAPα lacks an N-terminal extension as foundin POP. Moreover, the essential elements of the DP IV-dimerization motifare also present in FAPα, including the extension of strand 2 and 3 ofpropeller blade IV.

Functional role of oligomerization. The crystal structure shows thatdimerization is not required to complete the active site architecture ofDP IV, as for example in the case of tricorn (Brandstetter, H., Kim, J.-S., Groll, M. & Huber, R. (2001) Nature 414, 466-469.). Instead,dimerization and tetramerization will affect interaction with othercomponents, including proteolytic substrates and ADA and mediatecell-cell contacts. Moreover, dimerization of DP IV is likely to enhancethe receptor-ligand affinity by bivalent interaction. Finally, it islikely that dimerization is critical for signal transduction into thecell.

Substrate preference and catalytic mechanism. The hydrophobic S₁-pocketvisualizes that proline is perfectly suited as a P₁-residue, although itwill also fit other small uncharged residues such as alanine or serine.Interestingly, the S₁-site implements a mechanism to adapt to both iminoand amino acids in P₁-position. The hydroxyl Oθ of Tyr662 is able toform a hydrogen bond with the P₁-amide nitrogen and thus optimallypresents the substrate for catalysis. By contrast, the properorientation of proline in P₁-position is achieved by its side chaininteraction in addition to the binding to the oxyanion pocket. In thissituation, the hydroxyl of Tyr662 can slightly reorient to form ahydrogen bond with the side chain Oδ1 of Asn710, FIG. 26A. Therecognition of the P₂-residue is dictated by main chain interactionswith two prominent anchor sites, namely Glu205-Glu206 which form atwin-single salt bridge with the free amino terminus of the P₂-residue;and Arg125 together with Nδ2 of Asn710 which stabilize and activate theP₂-carbonyl oxygen. The Glu205-Glu2O6 motif is highly conserved in theDP IV gene family and it has been shown by site directed mutagenesis tobe essential for enzymatic activity. The role of the P₁oxyanion hole inactivating the substrate's scissile bond is well established for allproteases. In the case of DP IV as a post-proline processing enzyme anadditional requirement has to be met to achieve efficient catalysis.Proline containing peptides can adopt in solution also cis-peptide bondas well as trans-peptide bond conformation. However, as highlighted bythe inhibitor used in this invention, only a peptide intrans-conformation is able to productively bind to the active site.

β-propeller architecture: The tunnel through the eight-bladedβ-propeller widens from the surface towards the active site of DP IV.

Substrate access to and product egress from the active site. Twoopenings of similar diameter, but differing length, give access to theactive site. The situation in DP IV is most closely resembled by thetricom protease where a seven-bladed and six-bladed β-propeller providea separate entrance to and exit from the active site, respectively.Tricom protease is a serine protease with low but significant structuralhomology to the family of α/β-hydrolases. This similarity suggests thatthe β8-propeller provides substrate access to and the side openingproduct release from the DP IV active site. This tricom-derived model isable to explain the high substrate selectivity critical for DPIV-function to activate or inactivate regulatory peptides. Passagethrough the β-propeller tunnel requires the substrates to unfold therebyproviding their “finger print” to DP IV. Once the amino terminus of thepeptide approaches the active site, it is still held in place by itsC-terminus interacting with the β-propeller which then contributes toconformationally activate the substrate for cleavage. After thenucleophilic attack the acyl enzyme intermediate forms, while the primedproduct is directly released through the side exit.

Interaction with other components. DP IV binds adenosine deaminase (ADA)to the T-cell surface, thereby preventing the cell from adenosinemediated inhibition of proliferation. DP IV-ADA complex formation ispresumably hydrophobically driven, as the complex dissociates at verylow ionic strength. By using site-directed mutagenesis, Leu294 andVal341 were identified as two ADA binding sites (Abbott, C. A.,McCaughan, G. W., Levy, M. T., Church, W. B. & Gorrell, M. D. (1999)Eur. J Biochem. 226, 798-810.). Leu294 and Val341 are positioned at theouter strand of the tetramerization blade IV and blade V, respectively.Therefore, ADA-binding will interfere with tetramerization. Similarly,the glycosylation of Asn279 (Asn281 in the human sequence) is likely toinfluence ADA-binding. This teaches that tetramerization of DP IV andproper glycosylation of Asn279 serve as major control mechanism forADA-binding

DP IV as a target for drug design. The inhibitor structure used toestablish the crystal structure of DP IV in the present inventionidentified important recognition elements at DP IV's active site andrepresents an excellent starting point for rational design of activesite directed inhibitors. However, DP IV's involvement in a greatvariety of physiological processes poses a high challenge to avoidunwanted side effects for any DP IV drug development program. Ideally,it is possible now to target a particular DP IV substrate rather thanthe complete DP IV activity. Active site directed DP IV inhibitors,however, will interfere with the complete DP IV proteolytic activity andmight even interfere with structurally related members of the α-βhydrolase family. Non-active site directed inhibition strategies depicta solution to this problem. The sulfate bound to the oxyanion pocketwithin the β propeller tunnel formed by the amide nitrogens of Glu361and Ile407 and Nε2 of His363, as indicated in FIG. 26A, identified anexcellent target point for the development of inhibitors that blocksubstrate passage through the β propeller tunnel.

In the peptides, proteins and mutants shown, each encoded residue whereappropriate is represented by a one-letter or a three-letterdesignation, corresponding to the trivial name of the amino acid, inaccordance with usual practice. Examples of usual definitions are givenin the following conventional list: Amino Acid One-Letter SymbolThree-Letter Symbol Alanine A Ala Arginine R Arg Asparagine N AsnAspartic acid D Asp Cysteine C Cys Glutamine Q Gln Glutamic acid E GluGlycine G Gly Histidine H His Isoleucine I Ile Leucine L Leu Lysine KLys Methionine M Met Phenylalanine F Phe Proline P Pro Serine S SerThreonine T Thr Tryptophan W Trp Tyrosine Y Tyr Valine V ValSelenocysteine Sec

In a preferred embodiment of the present invention, a secondary bindingsite in the DP IV protein and/or DP IV-like enzymes is identified. Morepreferred, the existence of this secondary binding site can be used toinfluence the selectivity of the DP IV-catalyzed biodegradation of DPIV-substrates, e.g. alanine (GIP), proline (GRP) or serine (glucagon)substrates, dependent on the amino acid residue in the PI position anddependent on the tertiary structure of the DP IV-substrates. PreferredDP IV-substrates, the biodegradation whereof shall be regulatedaccording to the invention with compounds, which bind to the secondarybinding site, are serine substrates.

The regulation of the biodegradation of DP IV-substrates due tocompounds, which bind to the secondary binding site, is furtherdependent on the chain length of the substrates. Preferably, DPV-substrates have a chain length of more than 5 amino acid residues,more preferably more than 10 amino acid residues. Most preferred aresubstrates with more than 15 amino acid residues up to 70 amino acidresidues.

Currently known substrates of DP IV are:

-   -   Xaa-Pro peptides    -   Tyr-melanostatin    -   Endomorphin-2    -   Enterostatin    -   β-Casomorphin    -   Trypsinogen pro-peptide    -   Bradykinin    -   Substance P    -   Corticotropin-like intermediate lobe peptide    -   Gastrin-releasing peptide    -   Neuropeptide Y    -   Peptide YY    -   Aprotinin    -   RANTES    -   GCP-2    -   SDF-1α    -   SDF-1β    -   MDC    -   MCP-1    -   MCP-2    -   MCP-3    -   Eotaxin    -   IP-10    -   Insulin-like growth factor-I    -   Pro-colipase    -   Interleukin-2    -   Interleukin-1β    -   α₁-Microglobulin    -   Prolactin    -   Trypsinogen    -   Chorionic gonadotropin    -   Xaa-Ala peptides    -   PHM    -   GRH-(1-29)    -   GRH-(1-44)

GLP-1

-   -   GLP-2    -   Gastric inhibitory peptide    -   Orexin B    -   Xaa-Ser peptides    -   Orexin A

In the most preferred embodiment of the present invention, compounds forthe modulation of DP IV-catalyzed biodegradation of DP IV-substrates areprovided, which compounds bind to the secondary binding site of DP IV orDP IV-like enzymes. Such compounds are e.g. selected from the compoundsof the formulas a)-d):

Furthermore, the present invention provides agents, which bind to boththe active site and the secondary binding site of DP IV and DP IV-likeenzymes and thereby simultaneously modulate the enzyme activity andsubstrate specificity of DP IV or DP V-like enzymes.

DP IV is present in a wide variety of mammalian organs and tissues e.g.the intestinal brush-border ( Gutschmidt S . et al., “Insitu”—measurements of protein contents in the brush border region alongrat jejunal villi and their correlations with four enzyme activities.Histochemistry 1981, 72 (3), 467-79), exocrine epithelia, hepatocytes,renal tubuli, endothelia, myofibroblasts (Feller A. C. et al., Amonoclonal antibody detecting dipeptidylpeptidase IV in human tissue.Virchows Arch. A. Pathol. Anat. Histopathol. 1986; 409 (2):263-73),nerve cells, lateral membranes of certain surface epithelia, e.g.Fallopian tube, uterus and vesicular gland, in the luminal cytoplasm ofe.g., vesicular gland epithelium, and in mucous cells of Brunner's gland(Hartel S. et al., Dipeptidyl peptidase (DPP) IV in rat organs.Comparison of immunohistochemistry and activity histochemistry.Histochemistry 1988; 89 (2): 151-61), reproductive organs, e.g. caudaepididymis and ampulla, seminal vesicles and their secretions (Agrawal &Vanha-Perttula, Dipeptidyl peptidases in bovine reproductive organs andsecretions. Int. J. Androl. 1986, 9 (6): 435-52). In human serum, twomolecular forms of dipeptidyl peptidase are present (Krepela E. et al.,Demonstration of two molecular forms of dipeptidyl peptidase IV innormal human serum. Physiol. Bohemoslov. 1983, 32 (6): 486-96), theserum high molecular weight form of DP IV is expressed on the surface ofactivated T cells (Duke-Cohan J. S. et al., Serum high molecular weightdipeptidyl peptidase IV (CD26) is similar to a novel antigen DPPT-Lreleased from activated T cells. J. Immunol. 1996, 156 (5): 1714-21). Itis also a goal of the present invention to minimize possible sideeffects of currently available DP IV-inhibitors by the control andmanagement of the DP IV substrate specificity for the selectivetreatment of a DP IV mediated disease.

In another preferred embodiment of the present invention, all molecularforms, homologues and epitopes of proteins showing DP IV or DP IV-likeenzyme activity, from all mammalian tissues and organs, also of those,which are undiscovered yet, are intended to be embraced by the scope ofthis invention.

Among the rare group of proline-specific proteases, DP IV was originallybelieved to be the only membrane-bound enzyme specific for proline asthe penultimate residue at the amino-terminus of the polypeptide chain.However, other molecules, even structurally non-homologous with the DPIV but bearing corresponding enzyme activity, have been identified. DPIV-like enzymes, which are identified so far, are e.g. fibroblastactivation protein α, dipeptidyl peptidase IV β, dipeptidylaminopeptidase-like protein, N-acetylated α-linked acidic dipeptidase,quiescent cell proline dipeptidase, dipeptidyl peptidase II, attractinand dipeptidyl peptidase IV related protein (DPP 8), DPL1 (DPX, DP6),DPP 9 and DPL2 (DPP 10) are described in the review articles by Sedo &Malik (Sedo & Malik, Dipeptidyl peptidase IV-like molecules: homologousproteins or homologous activities? Biochimica et Biophysica Acta 2001,36506: 1-10) and Abbott & Gorrell (Abbott, C. A. & Gorrell, M. D., Thefamily of CD26/DP IV and related ectopeptidases. In: Langner & Ansorge(ed.), Ectopeptidases. Kluwer Academic/Plenum Publishers, New York,2002, pp. 171-195), and in Qi, S. Y., Cloning and characterization ofdipeptidyl peptidase 10, a new member of an emerging subgroup of serineproteases.

Another preferred embodiment of the present invention comprisesscreening methods for agents which bind to the secondary binding siteand/or modulate the selectivity and/or the activity of DP IV and/or DPIV-like enzymes. An agent according to the invention preferably binds toat least one secondary binding site of the DPIV or DP IV-like enzymeproteins.

The screening method for agents of the secondary binding site comprisesthe following steps:

-   -   a) Contacting at least one of that effectors with DP IV and/or a        DP IV-like enzyme, preferably under conditions which permit        binding there between;    -   b) Adding a substrate of DP IV and/or DP IV-like enzymes to said        DP IV and/or DP IV-like enzyme;    -   c) Monitoring the biodegradation of the substrate and/or        measuring the residual DP IV and/or DP IV-like enzyme activity;    -   d) Correlating changes in the biodegradation and/or enzyme        activity with the binding of said effectors to DP IV and/or DP        IV-like enzymes; and    -   e) Identification of selectivity and/or activity modifying        effectors.

The agents selected by the above described screening method can work byregulating (increasing or decreasing) the biodegradation of at least onesubstrate of DP IV or the DP IV-like enzyme, preferably by theprolongation of the half-life of such substrate, most preferably by theinhibition of the biodegradation of such substrate.

Conditions, under which binding between compounds and DP IV or DPIV-like enzymes are permitted, are described, e. g. in example 2.

DP IV or DP IV-like enzymes as used in the screening method describedabove mean purified DP IV or DP IV-like enzymes from mammals, selectedfrom but not restricted to human, monkey, mouse, rat etc., or DPIV or DPIV-like enzyme containing cells and cell lines from mammals, selectedfrom but not restricted to human, monkey, mouse, rat etc., or DP IV orDP IV-like enzyme containing cell extracts or body liquids e.g. liverextracts, blood plasma samples, blood serum samples, brain extractsetc., from such mammals.

Preferably, an agent increases the selectivity and/or activity of DP IVor DP IV-like enzymes towards substrates by at least about 10,preferably about 50, more preferably about 75, 90 or 100% relative tothe absence of the agent. More preferably, an agent increases theselectivity and/or activity of DP IV or DP IV-like enzymes towardsspecific substrates by at least about 10, preferably about 50, morepreferably about 75, 90 or 100% and prolongs the half live of thesubstrates in the serum or in the plasma of a mammal at least about 1fold, preferably about 2fold, more preferably about 3fold, 4fold orhigher relative to the absence of the agent. Most preferably, an agentincreases the selectivity and/or activity of DP IV or DP IV-like enzymesin such a way that the half live of at least one substrate in the serumor in the plasma of a mammal is increased at least about 1fold,preferably about 2fold, more preferably about 3fold, 4fold or higher,most preferably complete inhibition of the degradation of such asubstrate is achieved, relative to the absence of the agent.

It is also preferred according to the invention that the agents modulatethe interaction between DP IV or DP IV-like enzymes and binding proteinsthereof. Binding proteins are proteins that bind other proteins in anon-covalent manner and thereby modulate their activity or serve ascarriers of these proteins. Binding proteins of DP IV (CD26) identifiedso far include adenosine deaminase, two proteins of HIV, transactivatorprotein (tat) and the gp120 envelope protein, CD45, a membrane locatedtyrosine phosphatase, extracellular matrix proteins, such as collagenand fibronectin, plasminogen and streptokinase, mannose6-phosphat/insulin-like growth factor II receptor, the isoform NH3 ofthe Na⁺/H⁺ exchanger from renal microvilly membranes and the thromboxaneA2 receptor.

Especially preferred are compounds or agents that prevent and/or inhibitthe interaction between DP IV and/or DP IV-like enzymes and bindingproteins of these enzymes.

According to another embodiment of the present invention, theselectivity and/or activity modifying effectors block the productrelease site of DP IV and/or DP IV-like enzymes.

Further preferred are selectivity and/or activity modifying effectors,which prevent the tetramerization of DP IV and/or DP IV-like enzymes atthe cell surface between a soluble DP IV dimer pair or dimers located onthe surface of two different cells in a mammal.

Agents (also called compounds herein) can be pharmacological agentsalready known in the art or can be compounds previously unknown to haveany pharmacological activity. The compounds can be naturally occurringor designed in the laboratory. They can be isolated from microorganisms,animals, or plants, and can be produced recombinantly, or synthesized bychemical methods in the art. If desired, agents can be obtained usingany of the numerous combinatorial library methods known in the art,including but not limited to, biological libraries, spatiallyaddressable parallel solid phase or solution phase libraries, syntheticlibrary methods requiring deconvolution, the “one-bead-one-compound”library method, and synthetic library methods using affinitychromatography selection. The biological library approach is limited topolypeptide libraries, while the other four approaches are applicable topolypeptide, non-peptide oligomer, or small molecule libraries ofcompounds. See Lam, Anticancer Drug Des., 12, 145, 1997.

Methods for the synthesis of molecular libraries are well known in theart (see, for example, De Witt et al., Proc. Natl. Acad. Sci. USA 90,6909, 1993; Erb et al. Proc. Natl. Acad. Sci. USA 91, 11422, 1994;Zuckermann et al., J. Med. Chem. 37, 2678, 1994; Cho et al., Science261, 1303, 1993 ; Carell et al., Angew. Chem. Int. Ed. Engl. 33, 2059,1994; Carell et al., Angew. Chem. Int. ed. engl. 33, 2061; Gallop etal., J. Med. Chem. 37, 1233, 1994). Libraries of compounds can bepresent in solution (see, e.g. Houghten, Bio Techniques 13, 412421,1992) or on beads (Lam, nature 354, 824, 1991) chips (Fodor, Nature 364,555556, 1993) bacteria or spores (Ladner, U.S. Pat. No. 5,223,409),plasmids (Cull et al., Proc. Natl. Acad. Sci. USA 89, 198651869, 1992),or phage (Scott & Smith, Science 249, 386390, 1990; Devlin, Science 249,404406, 1990); Cwirla et la., Proc. Natl. Acad. Sci. 97, 63786382, 1990;Felici, J. Mol. Biol. 222, 301310, 1991; and Ladner, U.S. Pat. No.5,223,409).

High Throughput Screening

Agents can be screened for the ability to bind to DP IV or DP IV-likeenzymes or to affect DP IV or DP IV-like enzyme activity using highthroughput screening. Using high throughput screening, many discretecompounds can be tested in parallel so that large numbers of agents canbe quickly screened. The most widely established techniques utilize96-well microtiter plates. The well of the microtiter plates typicallyrequire assay volumes that range from 50 to 500 μl. In addition to theplates, many instruments, materials, pipettors, robotics, plate washers,and plate readers are commercially available to fit the 96-well format.

Alternatively, “Free format assays”, or assays that have no physicalbarrier between samples, can be used. For example, an assay usingpigment cells (melanocytes) in a simple homogeneous assay forcombinatorial peptide libraries is described by Jayawickreme et al.,Proc. Natl. Acad. Sci. USA 19, 161418 (1994).

Another example of a free format assay is described by Chelsky,“Strategies for Screening Combinatorial Libraries: Novel and TraditionalApproaches,” reported at the First Annual conference of The Society forBiomolecular Screening in Philadelphia, Pa. (Nov. 710, 1995). Chelskyplaced a simple homogenous enzyme assay for carbonic anhydrase inside anagarose gel such that the enzyme in the gel would cause a color changethroughout the gel. Thereafter, beads carrying combinatorial compoundswere partially released by UV LIGHT. Compounds that inhibited the enzymewere observed as local zones of inhibition having less color change.

Yet another example is described by Salomon et al., Molecular Diversity2, 5763 (1996). In this example, combinatorial libraries were screenedfor compounds that had cytotoxic effects on cancer cells growing inagar.

Another high throughput screening method is described in Beutel et al.,U.S. Pat. No. 5,976,813. In this method, test samples are placed in aporous matrix. One or more assay components are then placed within, ontop of, or at the bottom of a matrix such as a gel, a plastic sheet, afilter, or other form of easily manipulated solid support. When samplesare introduced to the porous matrix they diffuse sufficiently slowly,such that the assays can be performed without the test samples runningtogether.

Binding Assays

For binding assays, the agent is preferably a small molecule which bindsto and occupies, the secondary binding site of DP IV or DP IV-likeenzymes, such that normal biological activity is changed or prevented.Examples of such small molecules include, but are not limited to, smallpeptides or peptide like molecules.

In binding assays, either the agent of DP IV or the DP IV-like enzymecan comprise a detectable label, such as a fluorescent, radioisotopic,chemiluminescent, or the enzyme is labeled, such as horseradishperoxidase, alkaline phosphatase, or luciferase. Detection of an agent,which is bound to DP IV or the DP IV-like enzyme can then beaccomplished, for example, by direct counting of radioemmission, byscintillation counting, or by determining conversion of an appropriatesubstrate to a detectable product.

Alternatively, binding of an agent to DP IV or a DP IV-like enzyme canbe determined without labelling either of the interactants. For example,a microphysiometer can be used to detect binding of an agent with DP IVor a DP IV-like enzyme. A microphysiometer (e.g., Cytosensor™) is ananalytical instrument that measures the rate at which a cell acidifiesits environment using a light-addressable potentiometric sensor (LAPS).Changes in this acidification rate can be used as an indicator of theinteraction between an agent and DP IV or a DP IV-like enzyme (McConnelet al., Science 257, 19061912, 1992).

Determining the ability of an agent to bind to DP IV or a DP IV-likeenzyme also can be accomplished using a technology such as real-timeBiomolecular Interaction Analysis (BIA) (Sjolander & Urbaniczky, Anal.Chem. 63, 23382345, 1991, and Szabo et al., Curr. Opin. Struct. Biol. 5,699705, 1995) BIA is a technology for studying biospecific interactionsin real time, without labelling any of the interactants (e.g. BIAcore™).Changes in the optical phenomenon surface plasmon resonance (SPR) can beused as an indication of real-time reactions between biologicalmolecules.

In yet another aspect of the invention, DP IV or a DP IV-like enzyme canbe used as a “bait protein” in a two hybrid assay or three-hybrid assay(see, e.g. U.S. Pat. No. 5,283,317; Zervos et al., Cell 72, 223232,1993; Madura 920924, 193; Iwabuchi et al., Oncogene 8, 16931696, 1993;and Brent WO94/10300), to identify other proteins which bind to orinteract with the DP IV or the DP IV-like enzyme and modulate itsactivity.

The two hybrid system is based on the modular nature of mosttranscription factors, which consist of separable DNA binding andactivation domains. Briefly, the assay utilizes two different DNAconstructs. For example, in one construct, a polynucleotide encoding DPIV or a DP IV-like enzyme can be fused to a polynucleotide encoding theDNA binding domain of a known transcription factor (e.g. GAL4). In theother construct a DNA sequence that encodes an unidentified protein(“prey” or “sample”) can be fused to a polynucleotide that c odes forthe activation domain of the known transcription factor. If the “bait”and the “prey” proteins are able to interact in vivo to form an proteindependent complex, the DNA binding and activation domains of thetranscription factor are brought into close proximity. This proximityallows transcription of a reporter gene (e.g. LacZ), which is operablylinked to a transcriptional regulatory site responsive to thetranscription factor. Expression of the reporter gene can be detected,and cell colonies containing the functional transcription factor can beisolated and used to obtain the DNA sequence encoding the protein whichinteracts with the dipeptidyl-peptidase IV-like enzyme polypeptide.

It may be desirable to immobilize either the DP IV or DP IV-like enzymeor the agent to facilitate separation of bound from unbound forms of oneor both of the interactants, as-well-as to accommodate automation of theassay. Thus, either DP IV or the DP IV-like enzyme or the agent can bebound to a solid support. Suitable solid supports include, but are notlimited to, glass or plastic slices, tissue culture plates, microtiterwells, tubes, silicon chips, or particles such as beads (including, butnot limited to latex, polysterene, or glass beads). Any method known inthe art can be used to attach DP IV or the DP IV-like enzyme or agent toa solid support, including use of covalent and non-covalent linkages,passive absorption, or pairs of binding moieties attached respectivelyto the polypeptide or agent and the solid support. Agents are preferablybound to the solid support in an array, so that the location ofindividual test compounds can be tracked. Binding of a test compound toa DP IV or a DP IV-like enzyme can be accomplished in any vesselsuitable for containing the reactants. Examples of such vessels includemicrotiter plates, test tubes, and microcentrifuge tubes.

In one embodiment, the DP IV or DP IV-like enzyme is a fusion proteincomprising a domain that allows the DP IV or DP IV-like enzyme to bebound to a solid support. For example, glutathione-S-transferase fusionproteins can be absorbed onto glutathione sepharose beads (SigmaChemical, St. Louis, Mo.) or glutathione derivatized microtiter plates,which are then combined with the agent and the non-absorbed DP IV or DPIV-like enzyme; the mixture is then incubated under conditions conduciveto complex formation (e.g., at physiological conditions for salt andpH). Following incubation, the beads or microtiter plate wells arewashed to remove any unbound components. Binding of the interactants canbe determined either directly or indirectly, as described above.Alternatively, the complexes can be dissociated from the solid supportbefore binding is determined.

Other techniques for immobilizing proteins on a solid support also canbe used in the screening assays of the invention. For example, either DPIV or a DP IV-like enzyme or an agent can be immobilized utilizingconjugation of biotin and streptavidin. Biotinylated DP IV or DP IV-likeenzymes or agents can be prepared from biotin-NHS-(N-hydroxysuccinimide)using techniques well known in the art (e.g. biotinylation kit, PierceChemicals, Rockford, Ill.) and immobilized in the wells ofstreptavidin-coated 96 well plates (Pierce chemical). Alternatively,antibodies which specifically bind to DP IV, a DP IV-like enzyme or anagent, but which do not interfere with a desired binding site, such assecondary binding site or the active site of DP IV or the DP IV-likeenzyme, can be derivatized to the wells of the plate. Unbound targets orproteins can be trapped in the wells by antibody conjugation.

Examples for commercial available antibodies against DP IV or CD26 arefor instance: Species Company Clone (antigen) Application Host CoulterTa1 human IF, FACS Mouse Ba5 human FACS Biozol TA59 human ICH* (Endogen)Pharmingen M-A216 human IF, FACS Mouse Biotrend  13.4 rat ICH, IF MouseM-T099 human ICH, IF Mouse 134-2C2 human IF, FACS Mouse LT-27 human IF,FACS Mouse Biozol MRCOX-61 rat FC Mouse Biozol 236.3 rat IF, IPrep,IHstaining Mouse Research 202.36 human IF Mouse Diagnostics Research134-2C2 human T-cell signaling, HIV Mouse Diagnostics infection

Methods for detecting such complexes, in addition to those describedabove for the GST-immobilized complexes, include immunodetection ofcomplexes using antibodies which specifically bind to DP IV or DPIV-like enzymes or the agent, enzyme linked assays which rely ondetecting an activity of the DP IV or the DP IV-like enzyme, and SDS gelelectrophoresis under non-reducing conditions.

Screening for agents which bind to DP IV or a DP IV-like enzyme also canbe carried out in an intact cell. Any cell which comprises DP IV or a DPIV-like enzyme can be used in a cell-based assay system. DP IV or a DPIV-like enzyme can be naturally occurring in the cell or can beintroduced using techniques such as those described above. Binding ofthe agents to DP IV or a DP IV-like enzyme is determined as describedabove.

Enzyme Assays

Agents can be tested for the ability to increase or decrease theactivity of a mammalian DP IV or DP IV-like enzyme. DP IV activity canbe measured, for example, as described in U.S. Pat. No. 5,601,986 and,specific for the present invention, in examples 1 to 3.

Further on, a screening method for the identification and determinationof one or more secondary binding sites on DP IV and/or DP IV-likeenzymes is provided.

The screening method for secondary binding site(s) of DP IV and/or DPIV-like enzymes comprises the following steps:

-   -   a) Providing two or more different substrates, each having an        amino acid sequence, which binds to DP IV and/or DP IV-like        enzymes and aligning the amino acid sequences of said        substrates;    -   b) Identifying at least one consensus sequence amongst said        substrate amino acid sequences;    -   c) Synthesizing a peptide having said consensus sequence;    -   d) Contacting said synthesized peptide with DP IV and/or a DP        IV-like enzyme;    -   e) Adding a substrate of DP IV and/or a DP IV-like enzyme to the        DP IV and/or DP IV-like enzyme;    -   f) Monitoring the biodegradation of the substrate and/or        measuring the residual DP IV and/or DP IV-like enzyme activity;        and    -   g) Correlating changes in said biodegradation and/or enzyme        activity with the presence of a secondary binding site capable        of modulating the substrate specificity of DP IV and/or DP        IV-like enzymes.

Consensus sequences are highly conserved sequence segments. Preferredaccording to the invention are consensus sequences with the length of 3to 20 amino acids, more preferred of 5 to 12 amino acids, most preferred5 to 7 amino acids.

In another illustrative embodiment of the present invention, the agents,which bind to the secondary binding site, e.g. obtained or selected bythe screening method described herein, can be used alone or incombination with DP IV-inhibitors for the treatment of any type of DP IVmediated disorders, selected but not restricted to, impaired glucosetolerance, glucosuria, lipid disorders, dyslipidemia, hyperlipidaemia,hypertriglyceridemia, hypercholesterolemia, low HDL levels, high LDLlevels, metabolic acidosis, hyperglycemia, diabetes mellitus, diabeticneuropathy and nephropathy and of sequelae caused by diabetes mellitusin mammals, metabolism-related hypertension and cardiovascular sequelaecaused by hypertension in mammals, for the prophylaxis or treatment ofskin diseases and diseases of the mucosae, autoimmune diseases andinflammatory conditions, and for the treatment of psychosomatic,neuropsychiatric and depressive illnesses, such as anxiety, depression,sleep disorders, chronic fatigue, schizophrenia, epilepsy, nutritionaldisorders, spasm and chronic pain, atherosclerosis and its sequelae,vascular restenosis, irritable bowel syndrome, inflammatory boweldisease, including Crohn's disease and ulcerative colitis, otherinflammatory conditions, pancreatitis, abdominal obesity,neurodegenerative disease, retinopathy, nephropathy, Syndrome X, ovarianhyperandrogenism (polycystic ovarian syndrome), growth hormonedeficiency, neutropenia, tumor metastasis, benign prostatic hypertrophy,gingivitis, osteoporosis, and other conditions.

Agents such as N-(N′-substituted glycyl)-2-cyanopyrrolidines,L-threo-isoleucyl thiazolidine (P32/98), L-allo-isoleucyl thiazolidine,L-threo-isoleucyl pyrrolidine, and L-allo-isoleucyl pyrrolidine havebeen developed which inhibit the enzymatic activity of DP IV and aredescribed in U.S. Pat. No. 6,001,155, WO 99/61431, WO 99/67278, WO99/67279, DE 198 34 591, WO 97/40832, DE 196 16 486 C 2, WO 98/19998, WO00/07617, WO 99/38501, and WO 99/46272. Further examples of lowmolecular weight dipeptidyl peptidase IV inhibitors are agents such astetrahydroisoquinolin-3-carboxamide derivatives, N-substituted2-cyanopyroles and—pyrrolidines, N-(N′-substitutedglycyl)-2-cyanopyrrolidines, N-(substituted glycyl)-thiazolidines,N-(substituted glycyl)-4-cyanothiazolidines,amino-acyl-borono-prolyl-inhibitors and cyclopropyl-fused pyrrolidines.Inhibitors of dipeptidyl peptidase IV are described in U.S. Pat. No.6,380,398, U.S. Pat. No. 6,011,155; U.S. Pat. No. 6,107,317; U.S. Pat.No. 6,110,949; U.S. Pat. No. 6,124,305; U.S. Pat. No. 6,172,081; WO95/15309, WO 99/61431, WO 99/67278, WO 99/67279, DE 198 34 591, WO97/40832, DE 196 16 486 C 2, WO 98/19998, WO 00/07617, WO 99/38501, WO99/46272, WO 99/38501, WO 01/68603, WO 01/40180, WO 01/81337, WO01/81304, WO 01/55105, WO 02/02560 and WO 02/14271, WO 02/04610, WO02/051836, WO 02/068420, WO 02/076450; WO 02/083128, WO 02/38541, WO03/000180, WO03/000181, WO 03/000250, WO 0 3/002530, WO 03/002531, WO03/002553, WO 03/002593, WO 03/004496, WO 03/004498, WO 03/024965, WO03/024942, WO 03/035067, WO 03/037327, WO 03/035057, WO 03/045977, WO03/055881, WO 03/68748, WO 03/68757, WO 03/057666, WO 03057144, WO03/040174 and WO 03/033524, the teachings of which are hereinincorporated by reference in their entirety concerning these inhibitors,their uses, definition and their production. The goal of these agents isto inhibit DP IV, and by doing so, to relieve effectively any type of DPIV-mediated disease. The inventors of the present invention havesurprisingly found that such agents can be advantageously employed foran entirely different therapeutic purpose, then previously known bythose skilled in the art.

Preferred for the use in combination with agents binding to thesecondary binding site of DP IV or DP IV-like enzymes are DPIV-inhibitors such as valine pyrrolidide (Novo Nordisk), NVP-DPP728A(1-[[[2-[{5-cyanopyridin-2-yl}amino]ethyl]amino]acetyl]-2-cyano-(S)-pyrrolidine)(Novartis) as disclosed by Hughes et al., Biochemistry, 38 (36),11597-11603, 1999, LAF-237(1-[(3-hydroxy-adamant-1-ylamino)-acetyl]-pyrrolidine-2(S)-carbonitrile);disclosed by Hughes et al., Meeting of the American Diabetes Association2002, Abstract no. 272 or (Novartis), TSL-225(tryptophyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid), disclosedby Yamada et. al., Bioorg. & Med. Chem. Lett. 8 (1998), 1537-1540,2-cyanopyrrolidides and 4-cyanopyrrolidides as disclosed by Asworth etal., Bioorg. & Med. Chem. Lett., 6, No. 22, pp 1163-1166 and 2745-2748(1996), FE-999011, disclosed by Sudre et al., Diabetes 51 (5), pp1461-1469 (2002) (Ferring) and the compounds disclosed in WO 01/34594(Guilford), employing dosages as set out in the above references.

In one especially illustrative embodiment, the present invention relatesto the use of agents, which bind to the secondary binding site(s) of DPIV or DP IV-like enzymes in combination with dipeptide-like compoundsand compounds analogous to dipeptide compounds that are formed from anamino acid and a thiazolidine or pyrrolidine group, and salts thereof,referred to hereinafter as dipeptide-like compounds. Preferably theamino acid and the thiazolidine or pyrrolidine group are bonded with anamide bond.

Especially suitable for that purpose according to the invention aredipeptide-like compounds in which the amino acid is preferably selectedfrom a natural amino acid, such as, for example, leucine, valine,glutamine, glutamic acid, proline, isoleucine, asparagines and asparticacid.

The dipeptide-like compounds used according to the invention exhibit ata concentration (of dipeptide compounds) of 10 μM, a reduction in theactivity of plasma dipeptidyl peptidase IV or DP IV-analogous enzymeactivities of at least 10%, especially of at least 40%. Frequently areduction in activity of at least 60% or at least 70% is also required.Preferred agents may also exhibit a reduction in activity of a maximumof 20% or 30%.

Preferred compounds are N-valyl prolyl, O-benzoyl hydroxylamine, a lanylpyrrolidine, isoleucyl thiazolidine like L-allo-isoleucyl thiazolidine,L-threo-isoleucyl pyrrolidine and salts thereof, especially the fumaricsalts, and L-allo-isoleucyl pyrrolidine and salts thereof. Especiallypreferred compounds are glutaminyl pyrrolidine and glutaminylthiazolidine of formulas 1 and 2:

Further preferred compounds are given in Table 6.

The salts of the dipeptide-like compounds can be present in a molarratio of dipeptide (-analogous) component to salt component of 1:1 or2:1. Such a salt is, for example, (Ile-Thia)₂ fumaric acid. TABLE 6Structures of further preferred dipeptide compounds DP IV-inhibitorH-Asn-pyrrolidine H-Asn-thiazolidine H-Asp-pyrrolidineH-Asp-thiazolidine H-Asp(NHOH)-pyrrolidine H-Asp(NHOH)-thiazolidineH-Glu-pyrrolidine H-Glu-thiazolidine H-Glu(NHOH)-pyrrolidineH-Glu(NHOH)-thiazolidine H-His-pyrrolidine H-His-thiazolidineH-Pro-pyrrolidine H-Pro-thiazolidine H-Ile-azididine H-Ile-pyrrolidineH-L-allo-Ile-thiazolidine H-Val-pyrrolidine H-Val-thiazolidine

In another preferred embodiment, the present invention provides the useof agents binding to the secondary binding site(s) of DP IV or DPIV-like enzymes in combination with substrate-like peptide compounds offormula 3 useful for competitive modulation of dipeptidyl peptidase IVcatalysis:

wherein

A, B, C, D and E are independently any amino acid moieties includingproteinogenic amino acids, non-proteinogenic amino acids, L-amino acidsand D-amino acids and wherein E and/or D may be absent.

Further conditions regarding formula (3):

-   -   A is an amino acid except a D-amino acid,    -   B is an amino acid selected from Pro, Ala, Ser, Gly, Hyp,        acetidine-(2)-carboxylic acid and pipecolic acid,    -   C is any amino acid except Pro, Hyp, acetidine-(2)-carboxylic        acid, pipecolic acid and except N-alkylated amino acids, e.g.        N-methyl valine and sarcosine,    -   D is any amino acid or missing, and    -   E is any amino acid or missing,        or:    -   C is any amino acid except Pro, Hyp, acetidine-(2)-carboxylic        acid, pipecolic acid, except N-alkylated amino acids, e.g.        N-methyl valine and sarcosine, and except a D-amino-acid;    -   D is any amino acid selected from Pro, Ala, Ser, Gly, Hyp,        acetidine-(2)-carboxylic acid and pipecolic acid, and    -   E is any amino acid except Pro, Hyp, acetidine-(2)-carboxylic        acid, pipecolic acid and except N-alkylated amino acids, e.g.        N-methyl valine and sarcosine.

Examples of amino acids which can be used in the present invention are:L and D-amino acids, N-methyl-amino-acids; allo- and threo-forms of Ileand Thr, which can, e.g. be α-, β- or Ω-amino acids, whereof α-aminoacids are preferred.

Examples of amino acids throughout the claims and the description are:aspartic acid (Asp), glutamic acid (Glu), arginine (Arg), lysine (Lys),histidine (His), glycine (Gly), serine (Ser) and cysteine (Cys),threonine (Thr), asparagine (Asn), glutamine (Gln), tyrosine (Tyr),alanine (Ala), proline (Pro), valine (Val), isoleucine (Ile), leucine(Leu), methionine (Met), phenylalanine (Phe), tryptophan (Trp),hydroxyproline (Hyp), beta-alanine (beta-Ala), 2-amino octanoic acid(Aoa), azetidine-(2)-carboxylic acid (Ace), pipecolic acid (Pip),3-amino propionic, 4-amino butyric and so forth, alpha-aminoisobutyricacid (Aib), sarcosine (Sar), ornithine (Orn), citrulline (Cit),homoarginine (Har), t-butylalanine (t-butyl-Ala), t-butylglycine(t-butyl-Gly), N-methylisoleucine (N-MeIle), phenylglycine (Phg),cyclohexylalanine (Cha), norleucine (Nle), cysteic acid (Cya) andmethionine sulfoxide (MSO), Acetyl-Lys, modified amino acids such asphosphoryl-serine (Ser(P)), benzyl-serine (Ser(Bzl)) andphosphoryl-tyrosine (Tyr(P)), 2-aminobutyric acid (Abu),aminoethylcysteine (AECys), carboxymethylcysteine (Cmc), dehydroalanine(Dha), dehydroamino-2-butyric acid (Dhb), carboxyglutaminic acid (Gla),homoserine (Hse), hydroxylysine (Hyl), cis-hydroxyproline (cisHyp),trans-hydroxyproline (transHyp), isovaline (Iva), pyroglutamic acid(Pyr), norvaline (Nva), 2-aminobenzoic acid (2-Abz), 3-aminobenzoic acid(3-Abz), 4-aminobenzoic acid (4-Abz), 4-(aminomethyl)benzoic acid (Amb),4-(aminomethyl)cyclohexanecarboxylic acid (4-Amc), Penicillamine (Pen),2-Amino-4-cyanobutyric acid (Cba), cycloalkane-carboxylic aicds.

Examples of Ω-amino acids are e.g.: 5-Ara (aminoraleric acid), 6-Ahx(aminohexanoic acid), 8-Aoc (aminooctanoic aicd), 9-Anc (aminovanoicaicd), 10-Adc (aminodecanoic acid), 11-Aun (aminoundecanoic acid),12-Ado (aminododecanoic acid).

Further amino acids are: indanylglycine (Igl), indoline-2-carboxylicacid (Idc), octahydroindole-2-carboxylic acid (Oic), diaminopropionicacid (Dpr), diaminobutyric acid (Dbu), naphtylalanine (1-Nal), (2-Nal),4-aminophenylalanin (Phe(4-NH₂)), 4-benzoylphenylalanine (Bpa),diphenylalanine (Dip), 4-bromophenylalanine (Phe(4-Br)),2-chlorophenylalanine (Phe(2-C1)), 3-chlorophenylalanine (Phe(3-C1)),4-chlorophenylalanine (Phe(4-C1)), 3,4-chlorophenylalanine (Phe(3,4-C1₂)), 3- fluorophenylalanine (Phe(3-F)), 4-fluorophenylalanine(Phe(4-F)), 3,4- fluorophenylalanine (Phe(3,4-F2)),pentafluorophenylalanine (Phe(F₅)), 4-guanidinophenylalanine(Phe(4-guanidino)), homophenylalanine (hPhe), 3-jodophenylalanine(Phe(3-J)), 4 jodophenylalanine (Phe(4-J)), 4-methylphenylalanine(Phe(4-Me)), 4-nitrophenylalanine (Phe-4-NO₂)), biphenylalanine (Bip),4-phosphonomehtylphenylalanine (Pmp), cyclohexyglycine (Ghg),3-pyridinylalanine (3-Pal), 4-pyridinylalanine (4-Pal),3,4-dehydroproline (A-Pro), 4-ketoproline (Pro(4-keto)), thioproline(Thz), isonipecotic acid (Inp),1,2,3,4,-tetrahydroisoquinolin-3-carboxylic acid (Tic), propargylglycine(Pra), 6-hydroxynorleucine (NU(6-OH)), homotyrosine (hTyr),3-jodotyrosine (Tyr(3-J)), 3,5-dijodotyrosine (Tyr(3,5-J₂)),d-methyl-tyrosine (Tyr(Me)), 3-NO₂-tyrosine (Tyr(3-NO₂)),phosphotyrosine (Tyr(PO₃H₂)), alkylglycine, 1-aminoindane-1-carboxyacid, 2-aminoindane-2-carboxy acid (Aic),4-amino-methylpyrrol-2-carboxylic acid (Py),4-amino-pyrrolidine-2-carboxylic acid (Abpc),2-aminotetraline-2-carboxylic acid (Atc), diaminoacetic acid (Gly(NH₂)),diaminobutyric acid (Dab), 1,3-dihydro-2H-isoinole-carboxylic acid(Disc), homocylcohexylalanin (hCha), homophenylalanin (hPhe oder Hof),trans-3-phenyl-azetidine-2-carboxylic acid,4-phenyl-pyrrolidine-2-carboxylic acid,5-phenyl-pyrrolidine-2-carboxylic acid, 3-pyridylalanine (3-Pya),4-pyridylalanine (4-Pya), styrylalanine,tetrahydroisoquinoline-1-carboxylic acid (Tiq),1,2,3,4-tetrahydronorharmane-3-carboxylic acid (Tpi),β-(2-thienryl)-alanine (Tha).

Other amino acid substitutions for those encoded in the genetic code canalso be included in peptide compounds within the scope of the inventionand can be classified within this general scheme.

Proteinogenic amino acids are defined as natural protein-derived α-aminoacids. Non-proteinogenic amino acids are defined as all other aminoacids, which are not building blocks of common natural proteins.

The resulting peptides may be synthesized as the free C-terminal acid oras the C-terminal amide form. The free acid peptides or the amides maybe varied by side chain modifications. Such side chain modificationsinclude for instance, but are not restricted to, homoserine formation,pyroglutamic acid formation, disulphide bond formation, deamidation ofasparagine or glutamine residues, methylation, t-butylation,t-butyloxycarbonylation, 4-methylbenzylation, thioanysilation,thiocresylation, benzyloxyrnethylation, 4-nitrophenylation,benzyloxycarbonylation, 2-nitrobencoylation, 2-nitrosulphenylation,4-toluenesulphonylation, pentafluorophenylation, diphenylmethylation,2-chlorobenzyloxycarbonylation, 2,4,5-trichlorophenylation,2-bromobenzyloxycarbonylation, 9-fluorenylmethyloxycarbonylation,triphenylmethylation, 2,2,5,7,8,-pentamethylchroman-6-sulphonylation,hydroxylation, oxidation of methionine, formylation, acetylation,anisylation, benzylation, bencoylation, trifluoroacetylation,carboxylation of aspartic acid or glutamic acid, phosphorylation,sulphation, cysteinylation, glycolysation with pentoses, deoxyhexoses,hexosamines, hexoses or N-acetylhexosamines, famesylation,myristolysation, biotinylation, palmitoylation, stearoylation,geranylgeranylation, glutathionylation, 5′-adenosylation,ADP-ribosylation, modification with N-glycolylneuraminic acid,N-acetylneuraminic acid, pyridoxal phosphate, lipoic acid,4′-phosphopantetheine, or N-hydroxysuccinimide.

In the compounds of formula (3), the amino acid moieties A, B, C, D, andE are respectively attached to the adjacent moiety by amide bonds in ausual manner according to standard nomenclature so that theamino-terminus (N-terminus) of the amino acids (peptide) is drawn on theleft and the carboxyl-terminus of the amino acids (peptide) is drawn onthe right. (C-terminus).

Until the present invention by Applicants, known peptide substrates ofthe proline-specific serine protease dipeptidyl peptidase IV in vitroare the tripeptides Diprotin A (Ile-Pro-Ile), Diprotin B (Val-Pro-Leu)and Diprotin C (Val-Pro-Ile). Applicants have unexpectedly discoveredthat the compounds disclosed herein above and below act as substrates ofdipeptidyl peptidase IV in vivo in a mammal and, in pharmacologicaldoses, improve insulin sensitivity and islet signaling and alleviatepathological abnormalities of the metabolism of mammals such asglucosuria, hyperlipidaemia, metabolic acidosis and diabetes mellitus bycompetitive catalysis.

Preferred peptide compounds are listed in table 7. TABLE 7 Examples ofpeptide substrates Mass (exp.)¹ Peptide Mass (calc.) [M + H⁺] 2-Aminooctanoic acid-Pro-Ile 369.5 370.2 Abu-Pro-Ile 313.4 314.0 Aib-Pro-Ile313.4 314.0 Aze-Pro-Ile 311.4 312.4 Cha-Pro-Ile 381.52 382.0 Ile-Hyp-Ile356.45 358.2 Ile-Pro-allo-Ile 341.4 342.0 Ile-Pro-t-butyl-Gly 341.47342.36 Ile-Pro-Val 327.43 328.5 Nle-Pro-Ile 341.45 342.2 Nva-Pro-Ile327.43 328.2 Orn-Pro-Ile 342.42 343.1 Phe-Pro-Ile 375.47 376.2Phg-Pro-Ile 361.44 362.2 Pip-Pro-Ile 338.56 340.0 Ser(Bzl)-Pro-Ile405.49 406.0 Ser(P)-Pro-Ile 395.37 396.0 Ser-Pro-Ile 315.37 316.3t-butyl-Gly-Pro-D-Val 327.4 328.6 t-butyl-Gly-Pro-Gly 285.4 286.3t-butyl-Gly-Pro-Ile 341.47 342.1 t-butyl-Gly-Pro-Ile-amide 340.47 341.3t-butyl-Gly-Pro-t-butyl-Gly 341.24 342.5 t-butyl-Gly-Pro-Val 327.4 328.4Thr-Pro-Ile 329.4 330.0 Tic-Pro-Ile 387.46 388.0 Trp-Pro-Ile 414.51415.2 Tyr(P)-Pro-Ile 471.47 472.3 Tyr-Pro-allo-Ile 391.5 392.0Val-Pro-allo-Ile 327.4 328.5 Val-Pro-t-butyl-Gly 327.4 328.15Val-Pro-Val 313.4 314.0¹[M + H⁺] were determined by Electrospray mass spectrometry in positiveionization mode.t-butyl-Gly is defined as:

Ser(Bzl) and Ser(P) are defined as benzyl-serine and phosphoryl-serine,respectively. Tyr(P) is defined as phosphoryl-tyrosine.

Further preferred compounds, which can be used according to the presentinvention in combination with agents binding to the secondary bindingsite(s) of DP IV or DP IV-like enzymes, are peptidylketones of formula4:

and pharmaceutically acceptable salts thereof, wherein:

A is selected from the following structures:

wherein

-   -   X¹ is H or an acyl or oxycarbonyl group including an amino acid        residue, N-protected amino acid residue, a peptide residue or a        N-protected peptide residue,    -   X² is H, —(CH)_(m)—NH—C₅H₃N—Y with m=2-4 or —C₅H₃N—Y (a divalent        pyridyl residue) and Y is selected from H, Br, Cl, I, NO₂ or CN,    -   X³ is H or selected from an alkyl-, alkoxy-, halogen-, nitro-,        cyano- or carboxy-substituted phenyl or from an alkyl-, alkoxy-,        halogen-, nitro-, cyano- or carboxy-substituted pyridyl residue,    -   X⁴ is H or selected from an alkyl-, alkoxy-, halogen-, nitro-,        cyano- or carboxy-substituted phenyl or from an alkyl-, alkoxy-,        halogen-, nitro-, cyano- or carboxy-substituted pyridyl residue,    -   X⁵ is H or an alkyl, alkoxy or phenyl residue,    -   X⁶ is H or an alkyl residue,    -   for n=1

X is selected from: H, OR², SR², NR²R³, N⁺R²R³R⁴, wherein:

-   -   R² stands for acyl residues, which are optionally substituted        with alkyl, cycloalkyl, aryl or heteroaryl residues, or for        amino acid residues or peptidic residues, or alkyl residues,        which are optionally substituted with alkyl, cycloalkyl, aryl or        heteroaryl residues,    -   R³ stands for alkyl or acyl residues, wherein R² and R³ may be        part of a saturated or unsaturated carbocyclic or heterocyclic        ring,    -   R⁴ stands for alkyl residues, wherein R² and R⁴ or R³ and R⁴ may        be part of a saturated or unsaturated carbocyclic or        heterocyclic ring,    -   for n=0

X is selected from:

wherein

-   -   B stands for: O, S or NR⁵, wherein R⁵ is H, alkyl or acyl,    -   C, D, E, F, G, Y, K, L, M, Q, T, U, V and W are independently        selected from alkyl and substituted alkyl residues, oxyalkyl,        thioalkyl, aminoalkyl, carbonylalkyl, acyl, carbamoyl, aryl and        heteroaryl residues, and

Z is selected from H, or a branched or straight chain alkyl residue fromC₁-C₉, a branched or straight chain alkenyl residue from C₂-C₉, acycloalkyl residue from C₃-C₈, a cycloalkenyl residue from C₅-C₇, anaryl or heteroaryl residue, or a side chain selected from all sidechains of all natural amino acids or derivatives thereof.

In preferred compounds of formula 4, A is

wherein

-   -   X¹ is H or an acyl or oxycarbonyl group including an amino acid        residue, N-acylated amino acid residue, a peptide residue from        di- to pentapeptides, preferably a dipeptide residue, or a        N-protected peptide residue from di- to pentapeptides,        preferably a N-protected dipeptide residue    -   X² is H, —(CH)_(m)—NH—C₅H₃N—Y with m=2-4 or —C₅H₃N—Y (a divalent        pyridyl residue) and Y is selected from H, Br, Cl, I, NO₂ or CN,    -   for n=1

X is preferably selected from: H, OR², SR², NR²R³, wherein:

-   -   R stands for acyl residues, which are optionally substituted        with alkyl, cycloalkyl, aryl or heteroaryl residues, or for        amino acid residues or peptidic residues, or alkyl residues,        which are optionally substituted with alkyl, cycloalkyl, aryl or        heteroaryl residues,    -   R³ stands for alkyl or acyl residues, wherein R² and R³ may be        part of a saturated or unsaturated carbocyclic or heterocyclic        ring,    -   for n=0

X is preferably selected from:

wherein

-   -   B stands for: O, S or NR , wherein R⁵ is H, alkyl or acyl,    -   C, D, E, F, G, Y, K, L, M and Q are independently selected from        alkyl and substituted alkyl residues, oxyalkyl, thioalkyl,        aminoalkyl, carbonylalkyl, acyl, carbamoyl, aryl and heteroaryl        residues, and

Z is selected from H, or a branched or straight chain alkyl residue fromC₁-C₉, preferably C₂-C₆, a branched or straight chain alkenyl residuefrom C₂-C₉, a cycloalkyl residue from C₃-C₈, a cycloalkenyl residue fromC₅-C₇, an aryl or heteroaryl residue, or a side chain selected from allside chains of all natural amino acids or derivatives thereof

In more preferred compounds of formula 4, A is

wherein

-   -   X¹ is H or an acyl or oxycarbonyl group including an amino acid        residue, N-acylated amino acid residue or a peptide residue from        di- to pentapeptides, preferably a dipeptide residue, or a        N-protected peptide residue from di- to pentapeptides,        preferably a N-protected dipeptide residue    -   for n=1,

X is preferably selected from: H, OR², SR², wherein:

-   -   R² stands for acyl residues, which are optionally substituted        with alkyl or aryl residues,    -   for n=0

X is preferably selected from:

wherein

-   -   B stands for: O, S or NR⁵, wherein R⁵ is H, alkyl or acyl,    -   C, D, E, F, G, Y, K, L, M and Q are independently selected from        alkyl and substituted alkyl residues, oxyalkyl, thioalkyl,        aminoalkyl, carbonylalkyl, acyl, carbamoyl, aryl and heteroaryl        residues, and

Z is selected from H, or a branched or straight chain alkyl residue fromC₁-C₉, preferably C₂-C₆, a branched or straight chain alkenyl residuefrom C₂-C₉, a cycloalkyl residue from C₃-C₈, a cycloalkenyl residue fromC₅-C₇, an aryl or heteroaryl residue, or a side chain selected from allside chains of all natural amino acids or derivatives thereof.

In most preferred compounds of formula 4, A is

wherein

-   -   X¹ is H or an acyl or oxycarbonyl group including an amino acid        residue, N-acylated amino acid residue or a dipeptide residue,        containing a Pro or Ala in the penultimate position, or a        N-protected dipeptide residue containing a Pro or Ala in the        penultimate position,    -   for n=1,

X is H,

-   -   for n=0

X is preferably selected from:

wherein

-   -   B stands for: O or S, most preferably for S    -   C, D, E, F, G, Y, K, L, M, Q, are H and

Z is selected from H, or a branched or straight chain alkyl residue fromC₃-C₅, a branched or straight chain alkenyl residue from C₂-C₉, acycloalkyl residue from C₅-C₇, a cycloalkenyl residue from C₅-C₇, anaryl or heteroaryl residue, or a side chain selected from all sidechains of all natural amino acids or derivatives thereof.

Most preferred for Z is H.

According to a preferred embodiment the acyl groups are C₁-C₆-acylgroups.

According to a further preferred embodiment the alk(yl) groups areC₁-C₆-alk(yl) groups, which may be branched or unbranched.

According to a still further preferred embodiment the alkoxy groups areC₁-C₆-alkoxy groups.

According to yet another preferred embodiment the aryl residues areC₅-C₁₂ aryl residues that have optionally fused rings.

According to a still further preferred embodiment the cycloalkylresidues (carbocycles) are C₃-C₈-Cycloalkyl residues.

According to another preferred embodiment the heteroaryl residues areC₄-C₁₁ aryl residues that have optionally fused rings and, in at leastone ring, additionally from 1 to 4 preferably 1 or 2 hetero atoms, suchas O, N and/or S.

According to a further preferred embodiment peptide residues arecorresponding residues containing from 2 to 50 amino acids.

According to another preferred embodiment the heterocyclic residues areC₂-C₇-cycloalkyl radicals that additionally have from 1 to 4, preferably1 or 2 hetero atoms, such as O, N and/or S.

According to astill further preferred embodiment the carboxy groups areC₁-C₆ carboxy groups, which may be branched or unbranched.

According to yet another preferred embodiment the oxycarbonyl groups aregroups of the formula —O—(CH₂)₁₋₆COOH.

The amino acids can be any natural or synthetic amino acid, preferablynatural alpha amino acids.

Preferred compounds of formula (4) are2-Methylcarbonyl-1-N-[(L)-Alanyl-(L)-Valinyl]-(2S)-pyrrolidinehydrobromide;2-Methyl)carbonyl-1-N-[(L)-Valinyl-(L)-Prolyl-(L)-Valinyl]-(2S)-pyrrolidinehydrobromide;2-[(Acetyl-oxy-methyl)carbonyl]-1-N-[(L)-Alanyl-(L)-Valinyl]-(2S)-pyrrolidinehydrobromide;2-[Benzoyl-oxy-methyl)carbonyl]-1-N-[{(L)-Alanyl}-(L)-Valinyl]-(2S)-pyrrolidinehydrobromide;2-{[(2,6-Dichlorbenzyl)thiomethyl]carbonyl}-1-N-[{(L)-Alanyl}-(L)-Valinyl]-(2S)-pyrrolidine;2-[Benzoy-loxy-methyl)carbonyl]-1-N-[Glycyl-(L)-Valinyl]-(2S)-pyrrolidinehydrobromide;2-[([1,3]-thiazole-2-yl)carbonyl]-1-N-[{(L)-Alanyl}-(L)-Valinyl]-(2S)-pyrrolidinetrifluoracetat;2-[(benzothiazole-2-yl)carbonyl]-1-N-[N-{(L)-Alanyl}-(L)-Valinyl]-(2S)-pyrrolidintrifluoracetat;2-[(-benzothiazole-2-yl)carbonyl]-1-N-[{(L)-Alanyl}-Glycyl]-(2S)-pyrrolidinetrifluoracetat;2-[(pyridin-2-yl)carbonyl]-1-N-[N-{(L)-Alanyl}-(L)-Valinyl]-(2S)-pyrrolidinetrifluoracetat.

Further, according to the present invention compounds of formula (5)including all stereoisomers and pharmaceutical acceptable salts thereofcan be used in combination with agents binding to the secondary bindingsite(s) of DP IV or DP IV-like enzymes:B—(CH—R¹)_(n)—C(═X²)—D   (5)wherein

-   -   n is 0 or 1,    -   R¹ stands for H, C₁-C₉ branched or straight chain alkyl,        preferably H, n-butan-2-yl, n-prop-2-yl or isobutyl, C₂-C₉        branched or straight chain alkenyl, C₃-C₉ cycloalkyl, preferably        cyclohexyl, C₅-C₇ cycloalkenyl, aryl, heteroaryl or a side chain        of a natural amino acid or mimetics thereof,

X² stands for O, NR⁶, N⁺(R⁷)₂, or S,

B is selected from the following groups:

-   -   where X⁵ is H or an acyl or oxycarbonyl group including amino        acids,    -   R⁵ is H, C₁-C₉ branched or straight chain alkyl, preferably H,        n-butan-2-yl, n-prop-2-yl or isobutyl, C₂-C₉ branched or        straight chain alkenyl, C₃-C₉ cycloalkyl, preferably cyclohexyl,        3-hydroxyadamant-d-yl, C₅-C₇ cycloalkenyl, aryl, heteroaryl or a        side chain of a natural amino acid or derivatives thereof, or a        group of the formula —(CH)_(m)—NH—C₅H₃N—Y where m is an integer        of 2-4, —C₅H₃N—Y is a divalent pyridyl moiety and Y is a        hydrogen atom, a halogen atom, a nitro group or a cyano group,    -   R⁶, R⁷ R⁸ and R⁹ are independently selected from H, optionally        substituted C₁-C₉ branched or straight chain alkyl, preferably        an optionally substituted C₂-C₅ branched or straight chain        alkyl; or optionally substituted C₂-C₉ branched or straight        chain alkenyl, preferably an C₂-C₅ branched or straight chain        alkenyl; or optionally substituted C₃-C₈ cycloalkyl, preferably        an optionally substituted C₄-C₇ cycloalkyl; or an optionally        substituted C₅-C₇ cycloalkenyl, or an optionally substituted        aryl residue,    -   Z is selected from H, pyridyl or optionally substituted phenyl,        optionally substituted alkyl groups, alkoxy groups, halogens,        nitro, cyano and carboxy groups,    -   W is selected from H, pyridyl or optionally substituted phenyl,        optionally substituted alkyl groups, alkoxy groups, halogens,        nitro, cyano and carboxy groups,    -   W¹ is H or optionally substituted alkyl, alkoxy or optionally        substituted phenyl, and    -   Z¹ is H, or optionally substituted alkyl,    -   R³ and R⁴ are independently H, hydroxy, alkyl, alkoxy, aralkoxy,        nitro, cyano or halogen,    -   D is an optionally substituted compound of the formula        which can be saturated, or can have one, two or three double        bonds,        wherein    -   X⁸ to X¹¹ are independently CH, N, N⁺(R⁷), or CR⁸, if        unsaturated, or    -   X⁸ to X¹¹ are independently CH₂, NH, NH⁺(R⁷), O, or S if        saturated,    -   X¹² is CHA, NA, CH₂, NH, NH⁺(R⁷), or CHR⁸, if saturated or    -   X¹² is CA, NA⁺, CH, N, N⁺(R⁷), or CR⁸, if unsaturated and    -   A is H or an isoster of a carboxylic acid such as CN, SO₃H,        CONOH, PO₃R⁵R⁶, a tetrazole, an amide, an ester or an acid        anhydride.

Throughout the application, D contains preferably at most two, furtherpreferred at most one hetero atom in the ring.

According to preferred embodiments of the present invention, D standsfor optionally substituted C₄-C₇ cycloalkyl, preferably C₄-C₆cycloalkyl, optionally substituted C₄-C₇ cycloalkenyl, or optionallysubstituted (hetero)cycloalkyl of the formulae

wherein the residues are as defined above,or

that is, a five-membered ring containing one or two double bonds in thering,wherein the residues are as defined above,

wherein the residues are as defined above,

wherein the residues are as defined above,

that is a six-membered ring containing one or two double bonds in thering,wherein the residues are as defined above,

wherein the residues are as defined above.

According to a preferred embodiment, B has the following formula:

wherein the residues are as defined above.

According to another preferred embodiment, B has the following formula:

wherein the residues are as defined above.

Preferred compounds according to formula (5) are

-   -   1-cyclopentyl-3-methyl-1-oxo-2-pentanaminium chloride,    -   1-cyclopentyl-3-methyl-1-oxo-2-butanaminium chloride,    -   1-cyclopentyl-3,3-dimethyl-1-oxo-2-butanaminium chloride,    -   1-cyclohexyl-3,3-dimethyl-1-oxo-2-butanaminium chloride,    -   3-(cyclopentylcarbonyl)-1,2,3,4-tetrahydroisoquinolinium        chloride, and N-(2-cyclopentyl-2-oxoethyl)cyclohexanaminium        chloride.

Because of the wide distribution of the protein in the body and the widevariety of mechanisms involving DP IV, DP IV-activity and DP W-relatedproteins, systemic therapy (enteral or parenteral administration) withDP IV-inhibitors can result in a series of undesirable side-effects.

The problem to be solved was moreover, to provide compounds that can beused, in combination with agents binding to the secondary bindingsite(s) of DP IV or DP IV-like enzymes, for targeted influencing oflocally limited patho-physiological and physiological processes. Theproblem of the invention especially consists in obtaining locallylimited and highly specific inhibition of DP IV or DP IV-analogousactivity for the purpose of targeted intervention in the regulation ofthe activity of locally active substrates.

This problem is solved according to the invention by the use compoundsof the general formula (6) in combination with agents binding to thesecondary binding site(s) of DP IV or DP IV-like enzymes:

A is an amino acid having at least one functional group in the sidechain,

B is a chemical compound covalently bound to at least one functionalgroup of the side chain of A,

C is a thiazolidine, pyrrolidine, cyanopyrrolidine, hydroxyproline,dehydroproline or piperidine group amide-bonded to A.

In accordance with a preferred embodiment of the invention,pharmaceutical compositions are used comprising at least one compound ofthe general formula (6) and at least one customary adjuvant appropriatefor the site of action.

Preferably A is an α-amino acid, especially a natural α-amino acidhaving one, two or more functional groups in the side chain, preferablythreonine, tyrosine, serine, arginine, lysine, aspartic acid, glutamicacid or cysteine.

Preferably B is an oligopeptide having a chain length of up to 20 aminoacids, a polyethylene glycol having a molar mass of up to 20 000 g/mol,an optionally substituted organic amine, amide, alcohol, acid oraromatic compound having from 8 to 50 C atoms.

Despite an extended side chain function, the compounds of formula (6)can still bind to the active centre of the enzyme dipeptidyl peptidaseIV and analogous enzymes but are no longer actively transported by thepeptide transporter PepT1. The resulting reduced or greatly restrictedtransportability of the compounds according to the invention leads tolocal or site directed inhibition of DP IV and DP IV-like enzymeactivity.

By extending/expanding the side chain modifications, for example beyonda number of seven carbon atoms, it is accordingly possible to obtain adramatic reduction in transportability. With increasing spatial size ofthe side chains, there is a reduction in the transportability of thesubstances. By spatially and sterically expanding the side chains, forexample beyond the atom group size of a monosubstituted phenyl radical,hydroxylamine radical or amino acid residue, it is possible according tothe invention to modify or suppress the transportability of the targetsubstances.

Preferred compounds of formula (6) are compounds, wherein theoligopeptides have chain lengths of from 3 to 15, especially from 4 to10, amino acids, and/or the polyethylene glycols have molar masses of atleast 250 g/mol, preferably of at least 1500 g/mol and up to 15 000g/mol, and/or the optionally substituted organic amines, amides,alcohols, acids or aromatic compounds have at least 12 C atoms andpreferably up to 30 C atoms.

The compounds of the present invention can be converted into and used asacid addition salts, especially pharmaceutically acceptable acidaddition salts. The pharmaceutically acceptable salt generally takes aform in which an amino acids basic side chain is protonated with aninorganic or organic acid. Representative organic or inorganic acidsinclude hydrochloric, hydrobromic, perchloric, sulfuric, nitric,phosphoric, acetic, propionic, glycolic, lactic, succinic, maleic,fumaric, malic, tartaric, citric, benzoic, mandelic, methanesulfonic,hydroxyethanesulfonic, benzenesulfonic, oxalic, pamoic,2-naphthalenesulfonic, p-toulenesulfonic, cyclohexanesulfamic,salicylic, saccharinic or trifluoroacetic acid. All pharmaceuticallyacceptable acid addition salt forms of the compounds of formulas (1) to(6) are intended to be embraced by the scope of this invention.

In view of the close relationship between the free compounds and thecompounds in the form of their salts, whenever a compound is referred toin this context, a corresponding salt is also intended, provided such ispossible or appropriate under the circumstances.

The present invention further includes within its scope prodrugs of thecompounds of formulas (1) to (6). In general, such prodrugs will befunctional derivatives of the compounds which are readily convertible invivo into the desired therapeutically active compound. Thus, in thesecases, the present invention shall encompass the treatment of thevarious disorders described with prodrug versions of one or more of theclaimed compounds, which convert to the above specified compound in vivoafter administration to the subject. Conventional procedures for theselection and preparation of suitable prodrug derivatives are described,for example, in “Design of Prodrugs”, ed. H. Bundgaard, Elsevier, 1985and the patent applications DE 198 28 113 and DE 198 28 114, which arefully incorporated herein by reference.

Where the compounds or prodrugs according to this invention have atleast one chiral center, they may accordingly exist as enantiomers.Where the compounds or prodrugs possess two or more chiral centers, theymay additionally exist as diastereomers. It is to be understood that allsuch isomers and mixtures thereof are encompassed within the scope ofthe present invention. Furthermore, some of the crystalline forms of thecompounds or prodrugs may exist as polymorphs and as such are intendedto be included in the present invention. In addition, some of thecompounds may form solvates with water (i.e. hydrates) or common organicsolvents, and such solvates are also intended to be encompassed withinthe scope of this invention.

The compounds, including their salts, can also be obtained in the formof their hydrates, or include other solvents used for theircrystallization.

A further preferred embodiment of the present invention comprisescompounds capable of binding to the secondary binding site of DP IV orDP IV-like enzymes according to any one of the embodiments of thepresent invention

-   -   in combination with acarbose, or    -   in combination with metformin; or    -   in combination with acarbose and metformin.

In a further preferred embodiment, the compounds capable of binding tothe secondary binding site of DP IV and/or DP IV-like enzymes of thepresent invention, can be used in combination with at least oneantidiabetic agent selected from the group consisting of:

-   -   insulin sensitizers selected from the group consisting of        -   PPAR agonists,        -   biguanides, and        -   protein tyrosin phosphatase-1B (PTP-1B) inhibitors;    -   insulin and insulin mimetics;    -   sulfonylureas and other insulin secretagogues;    -   α-glucosidase inhibitors, e.g. acarbose;    -   glucagon receptor agonists;    -   GLP-1; GLP-1 mimetics, and GLP-1 receptor agonists;    -   GLP-2; GLP-2 mimetics, and GLP-2 receptor agonists, e.g. ALX-600        (teduglutide from NPS Allelix Corp.);    -   exendin-4 and exendin-4 mimetics, e.g. exenatide (AC-2993,        synthetic exendin-4 from Amylin/Eli Lilly);    -   GIP, GIP mimetics, and GIP receptor agonists;    -   PACAP, PACAP mimetics, and PACAP receptor 3 agonists;    -   PYY, PYY mimetics, PYY receptor agonists, and PYY receptor        antagonists,    -   cholesterol lowering agents selected from the group consisting        of        -   HMG-CoA reductase inhibitors,        -   sequestrants,        -   nicotinyl alkohol, nicotinic acid and salts thereof,        -   PPARα agonists,        -   PPARγ agonists,        -   PPARα/γ dual agonists,        -   inhibitors of cholesterol absorption,        -   acyl CoA:cholesterol acyltransferase inhibitors, and        -   antioxidants;    -   PPARδ agonists;    -   antiobesity compounds;    -   an ileal bile acid transporter inhibitor; and    -   anti-inflammatory agents.

A further preferred embodiment of the present invention comprisescompounds capable of binding to the secondary binding site of DP IV orDP IV-like enzymes according to any one of the embodiments of thepresent invention mentioned above

-   -   in combination with a gene therapeutic expression system for        GLP-1 comprising a viral vector comprising        -   (a) a polynucleotide sequence encoding GLP-1 (gluacogen like            peptide-1); and        -   (b) a polynucleotide sequence encoding a signal sequence            upstream of (a); and        -   (c) a polyadenylation signal downstream of (a); and        -   (d) a polynucleotide sequence encoding a proteolytic            cleavage site located between the polynucleotide sequence            encoding GLP-1 and the polynucleotide sequence encoding the            signal sequence; and        -   (e) wherein the expression of GLP-1 underlies a constitutive            promoter or is controlled by a regulatable promotor;        -   (f) wherein, optionally, the viral vector comprises a            polynucleotide sequence encoding GIP (glucose dependent            insulinotropic peptide);        -   (g) wherein, optionally, the viral vector is encompassed by            a mammalian cell. and /or    -   in combination with a gene therapeutic expression system for GIP        comprising a viral vector comprising        -   (a) a polynucleotide sequence encoding GIP (glucose            dependent insulinotropic peptide); and        -   (b) a polynucleotide sequence encoding a signal sequence            upstream of (a); and        -   (c) a polyadenylation signal downstream of (a); and        -   (d) a polynucleotide sequence encoding a proteolytic            cleavage site located between the polynucleotide sequence            encoding GIP and the polynucleotide sequence encoding the            signal sequence; and        -   (e) wherein the expression of GIP underlies a constitutive            promoter or is controlled by a regulatable promotor;        -   (f) wherein, optionally, the viral vector comprises a            polynucleotide sequence encoding GLP-1 (glucagon like            peptide 1);

(g) wherein, optionally, the viral vector is encompassed by a mammaliancell.

A further preferred embodiment of the present invention comprises thecompounds capable of binding to the secondary binding site of DP IV orDP IV-like enzymes in combination with a gene therapeutic expressionsystem for GLP-1 and/or GIP according to any one of the embodiments ofthe present invention mentioned above wherein

-   -   the signal sequence upstream of the gene of interest (GLP-1;        GIP) is the murine immunoglobulin K signal sequence or the glia        monster exendin signal sequence; and/or    -   the polyadenylation signal downstream of the gene of interest        (GLP-1; GIP) is derived from simian viraus 40 (SV 40); and /or    -   the proteolytic cleavage site is cleaved by furin preotease;        and/ or    -   the gene delivery vector for expression the gene of interest is        an adenoviral, retroviral, leniviral, adeno associated viral        vector; and /or    -   the constitutive promoter is a cytomegalovirus (CMV) promotor,        or a Rous sarcoma long-terminal repeat (LTR) sequence, and the        SV 40 early gene gene promoter; and the inducible promoter is        the Tet-On™/Tet-Off™ system available from Clontech; and /or    -   the mammalian cell is a primate or rodent cell, preferably a        human cell, more preferably a human hepatocyte.

In a further illustrative embodiment, the present invention providesformulations for agents binding to the secondary binding site of DP IVor DP IV-like enzymes allone or in combination with DP IV-inhibitors,e.g. the compounds of formulas (1) to (6), and their correspondingpharmaceutically acceptable prodrugs and acid addition salt forms, inpharmaceutical compositions. 7

To prepare the pharmaceutical compositions of this invention, one ormore compounds capable of binding to the secondary binding site and/orDP IV-inhibitors or salts thereof of the invention can be used as theactive ingredient(s). The active ingredient(s) is intimately admixedwith a pharmaceutical carrier according to conventional pharmaceuticalcompounding techniques, which carrier may take a wide variety of formsdepending of the form of preparation desired for administration, e.g.,oral or parenteral such as intramuscular. In preparing the compositionsin oral dosage form, any of the usual pharmaceutical media may beemployed. Thus, for liquid oral preparations, such as for example,suspensions, elixirs and solutions, suitable carriers and additivesinclude water, glycols, oils, alcohols, flavoring agents, preservatives,coloring agents and the like; for solid oral preparations such as, forexample, powders, capsules, gelcaps and tablets, suitable carriers andadditives include starches, sugars, diluents, granulating agents,lubricants, binders, disintegrating agents and the like. Because oftheir ease in administration, tablets and capsules represent the mostadvantageous oral dosage unit form, in which case solid pharmaceuticalcarriers are obviously employed. If desired, tablets may be sugar coatedor enteric coated by standard techniques. For parenterals, the carrierwill usually comprise sterile water, through other ingredients, forexample, for purposes such as aiding solubility or for preservation, maybe included.

Injectable suspensions may also prepared, in which case appropriateliquid carriers, suspending agents and the like may be employed. Thepharmaceutical compositions herein will contain, per dosage unit, e.g.,tablet, capsule, powder, injection, teaspoonful and the like, an amountof the active ingredient(s) necessary to deliver an effective dose asdescribed above. The pharmaceutical compositions herein will contain,per dosage unit, e.g., tablet, capsule, powder, injection, suppository,teaspoonful and the like, from about 0.03 mg to 100 mg/kg (preferred0.1-30 mg/kg) and may be given at a dosage of from about 0.1-300 mg/kgper day (preferred 1-50 mg/kg per day) of each active ingredient orcombination thereof The dosages, however, may be varied depending uponthe requirement of the patients, the severity of the condition beingtreated and the compound being employed. The use of either dailyadministration or post-periodic dosing may be employed.

Preferably these compositions are in unit dosage forms from such astablets, pills, capsules, powders, granules, sterile parenteralsolutions or suspensions, metered aerosol or liquid sprays, drops,ampoules, autoinjector devices or suppositories; for oral parenteral,intranasal, sublingual or rectal administration, or for administrationby inhalation or insufflation. Alternatively, the composition may bepresented in a form suitable for once-weekly or once-monthlyadministration; for example, an insoluble salt of the active compound,such as the decanoate salt, may be adapted to provide a depotpreparation for intramuscular injection. For preparing solidcompositions such as tablets, the principal active ingredient is mixedwith a pharmaceutical carrier, e.g. conventional tableting ingredientssuch as corn starch, lactose, sucrose, sorbitol, talc, stearic acid,magnesium stearate, dicalcium phosphate or gums, and otherpharmaceutical diluents, e.g. water, to form a solid preformulationcomposition containing a homogeneous mixture of a compound of thepresent invention, or a pharmaceutically acceptable salt thereof. Whenreferring to these preformulation compositions as homogeneous, it ismeant that the active ingredient is dispersed evenly throughout thecomposition so that the composition may be readily subdivided intoequally effective dosage forms such as tablets, pills and capsules. Thissolid preformulation composition is then subdivided into unit dosageforms of the type described above containing from 0.1 to about 500 mg ofeach active ingredient or combinations thereof of the present invention.

The tablets or pills of the compositions of the present invention can becoated or otherwise compounded to provide a dosage form affording theadvantage of prolonged action. For example, the tablet or pill cancomprise an inner dosage and an outer dosage component, the latter beingin the form of an envelope over the former. The two components can beseparated by an enteric layer which serves to resist disintegration inthe stomach and permits the inner component to pass intact into theduodenum or to be delayed in release. A variety of material can be usedfor such enteric layers or coatings, such materials including a numberof polymeric acids with such materials as shellac, cetyl alcohol andcellulose acetate.

This liquid forms in which the compositions of the present invention maybe incorporated for administration orally or by injection include,aqueous solutions, suitably flavoured syrups, aqueous or oilsuspensions, and flavoured emulsions with edible oils such as cottonseedoil, sesame oil, coconut oil or peanut oil, as well as elixirs andsimilar pharmaceutical vehicles. Suitable dispersing or suspendingagents for aqueous suspensions, include synthetic and natural gums suchas tragacanth, acacia, alginate, dextran, sodium carboxymethylcellulose,methylcellulose, polyvinylpyrrolidone or gelatin.

Where the processes for the preparation of the compounds according tothe invention give rise to mixture of stereoisomers, these isomers maybe separated by conventional techniques such as preparativechromatography. The compounds may be prepared in racemic form, orindividual enantiomers may be prepared either by enantiospecificsynthesis or by resolution. The compounds may, for example, be resolvedinto their components enantiomers by standard techniques, such as theformation of diastereomeric pairs by salt formation with an opticallyactive acid, such as (−)-di-p-toluoyl-d-tartaric acid and/or(+)-di-p-toluoyl-1-tartaric acid followed by fractional crystallizationand regeneration of the free base. The compounds may also resolved byformation of diastereomeric esters or amides, followed bychromatographic separation and removal of the chiral auxiliary.Alternatively, the compounds may be resolved using a chiral HPLC column.

During any of the processes for preparation of the compounds of thepresent invention, it may be necessary and/or desirable to protectsensitive or reactive groups on any of the molecules concerned. This maybe achieved by means of conventional protecting groups, such as thosedescribed in Protective Groups in Organic Chemistry, ed. J. F. W.McOmie, Plenum Press, 1973; and T. W. Greene & P. G. M. Wuts, ProtectiveGroups in Organic Synthesis, John Wiley & Sons, 1991. The protectinggroups may be removed at a convenient subsequent stage usingconventional methods known from the art.

The method of treating conditions modulated by the dipeptidyl peptidaseIV or dipeptidyl peptidase IV-like enzymes described in the presentinvention may also be carried out using a pharmaceutical compositioncomprising any compound or any combination of the compounds as definedherein and a pharmaceutically acceptable carrier. The pharmaceuticalcomposition may contain between about 0.01 mg and 100 mg, preferablyabout 5 to 50 mg, of each compound, and may be constituted into any formsuitable for the mode of administration selected. Carriers includenecessary and inert pharmaceutical excipients, including, but notlimited to, binders, suspending agents, lubricants, flavorants,sweeteners, preservatives, dyes, and coatings. Compositions suitable fororal administration include solid forms, such as pills, tablets,caplets, capsules (each including immediate release, timed release andsustained release formulations), granules, and powders, and liquidforms, such as solutions, syrups, elixirs, emulsions, and suspensions.Forms useful for parenteral administration include sterile solutions,emulsions and suspensions.

Advantageously, compounds of the present invention may be administeredin a single daily dose, or the total daily dosage may be administered individed doses of two, three or four times daily. Furthermore, compoundsfor the present invention can be administered in intranasal form viatopical use of suitable intranasal vehicles, or via transdermal skinpatches well known to those of ordinary skill in that art. To beadministered in the form of transdermal delivery system, the dosageadministration will, of course, be continuous rather than intermittentthroughout the dosage regimen.

For instance, for oral administration in the form of a tablet orcapsule, the active drug component can be combined with an oral,non-toxic pharmaceutically acceptable inert carrier such as ethanol,glycerol, water and the like. Moreover, when desired or necessary,suitable binders; lubricants, disintegrating agents and coloring agentscan also be incorporated into the mixture. Suitable binders include,without limitation, starch, gelatin, natural sugars such as glucose orbetalactose, corn sweeteners, natural and synthetic gums such as acacia,tragacanth or sodium oleate, sodium stearate, magnesium stearate, sodiumbenzoate, sodium acetate, sodium chloride and the like. Disintegratorsinclude, without limitation, starch, methyl cellulose, agar, bentonite,xanthan gum and the like.

The liquid forms in suitable flavored suspending or dispersing agentssuch as the synthetic and natural gums, for example, tragacanth, acacia,methyl-cellulose and the like. For parenteral administration, sterilesuspensions and solutions are desired. Isotonic preparations whichgenerally contain suitable preservatives are employed when intravenousadministration is desired.

The compounds of the present invention can also be administered in theform of liposome delivery systems, such as small unilamellar vesicles,large unilamellar vesicles, and multilamellar vesicles. Liposomes can beformed from a variety of phospholipids, such as cholesterol,stearylamine or phosphatidylcholines.

Compounds of the present invention may also be delivered by the use ofmonoclonal antibodies as individual carriers to which the compoundmolecules are coupled. The compounds of the present invention may alsobe coupled with soluble polymers as targetable drug carriers. Suchpolymers can include polyvinylpyrrolidone, pyran copolymer,polyhydroxypropylmethacrylamidephenol,polyhydroxyethylaspartamid-ephenol, or polyethyl eneoxidepolyllysinesubstituted with palmitoyl residue. Furthermore, the compounds of thepresent invention may be coupled to a class of biodegradable polymersuseful in achieving controlled release of a drug, for example, polyacticacid, polyepsilon caprolactone, polyhydroxy butyeric acid,polyorthoesters, polyacetals, polydihydropyrans, polycyanoacrylates andcross-linked or amphipathic block copolymers of hydrogels.

Compounds of this invention may be administered in any of the foregoingcompositions and according to dosage regimens established in the artwhenever treatment of the addressed disorders is required.

The daily dosage of the products may be varied over a wide range from0.01 to 1.000 mg per mammal per day. For oral administration, thecompositions are preferably provided in the form of tablets containing,0.01, 0.05, 0.1, 0.5, 1.0, 2.5, 5.0, 10.0, 15.0, 25.0, 50.0, 100, 150,200, 250 and 500 milligrams of each active ingredient or combinationsthereof for the symptomatic adjustment of the dosage to the patient tobe treated. An effective amount of the drug is ordinarily supplied at adosage level of from about 0.1 mg/kg to about 300 mg/kg of body weightper day. Preferably, the range is from about 1 to about 50 mg/kg of bodyweight per day. The compounds may be administered on a regimen of 1 to 4times per day.

Optimal dosages to be administered may be readily determined by thoseskilled in the art, and will vary with the particular compound used, themode of administration, the strength of the preparation, the mode ofadministration, and the advancement of disease condition. In addition,factors associated with the particular patient being treated, includingpatient age, weight, diet and time of administration, will result in theneed to adjust dosages.

EXAMPLES Example 1

Determination of the Half-Life (t_(1/2))

Matrix-assisted laser-desorption ionization time of flight massspectrometry (MALDI-TOF MS) experiments were carried out at 30° C. at pH7.6 in 0.1 M Tris/HCl (Sigma-Aldrich, Deisenhofen, Germany) buffer with25 μM peptide solution. The degradation fate of peptides was measured bymonitoring the signal intensity of the pseudomolecular ion peaks ofparent peptides and N-terminal shorted peptides versus time whenincubated with 40 mU procine DP IV, recombinant human DP IV or serum DPIV activity. The enzyme was preincubated with hexapeptide TFTSDY orTFTDDY or the heptapeptide H-Ser-D-Glu-Thr-Gly-D-Val-D-Lys-D-Val-OH (15min, 30° C., 0,016M, 1:1 with DP IV, the concentration of thehexapeptide or the heptapeptide in the reaction mixture was 160 μM). Ascontrol served the preincubation of DP IV with 0.01M Tris-buffer(Sigma-Aldrich, Deisenhofen, Germany). The mass spectrometer employedwas a Hewlett-Packard G2025 model with a linear time of flight analyzer;samples (4 μL) were mixed 1:1 v/v with matrix (44 mgdiammonium-hydrogen-citrate and 30 mg 2′,6′-dihydroxyacetophenone in 1ml aqueous solution containing 50% acetonitrile and 0.05%trifluoroacetic acid; Sigma-Aldrich), transferred to a probe tip andimmediately evaporated using the Hewlett-Packard G2024A(Hewlett-Packard, Waldbronn, Germany) sample preparation vacuum chamber.250 single laser-shot spectra were accumulated. This method ofmonitoring biodegradation has been validated and allows the generalcomparison of half-degradation times (t_(1/2)) under various conditions.

The t_(1/2)- calculation followed this procedure:

The height of the substrate peak was measured and set as 100% at time=0.During the reaction course the sum of substrate and product peak heightwere set as 100% and the percentage of the remaining substrate peak(also expressed as relative concentration) was determined. Diagrammedrelative substrate concentration versus time t_(1/2) can be calculatedbased on first order exponential decay reaction course.$A\overset{k_{l}}{\longrightarrow}B$ $\begin{matrix}{v = {{- \frac{\mathbb{d}\lbrack A\rbrack}{\mathbb{d}\lbrack t\rbrack}} = {{k_{l}*\lbrack A\rbrack} -}}} \\{{\int_{A_{0}}^{A_{1}}\quad\frac{\mathbb{d}\lbrack A\rbrack}{\lbrack A\rbrack}} = {\int_{t_{0}}^{t}{k_{1}\quad{\mathbb{d}t}}}} \\{\lbrack A\rbrack = {\lbrack A\rbrack_{0}{\mathbb{e}}^{{- k_{l}}t}}} \\{k_{l}\frac{\ln 2}{t_{1/2}}}\end{matrix}$

Legend:

-   -   A substrate (bioactive peptide)    -   B product (N-terminal truncated bioactive peptide)    -   K_(i) first order rate constant    -   K_(m) Michaelis-Menten-constant    -   v_(i) initial rate of the reaction    -   V_(max) maximal rate of the reaction    -   [S] substrate concentration

Example 2

Determination of K_(i):

In order to measure the inhibition constant K_(i) a photometric assaywas used The peptides were measured as competitors of the standardsubstrate GP-4-Nitroanilide. Three different substrate concentrations(0.4 mM to 0.05 mM) were combined with 8 different competitorconcentrations (0.5 mM to 2 μM). The reaction was started by addition of3.5 nM DP IV. Experiments were carried out under standard conditions:30° C. in pH 7.6 40 mM HEPES (Sigma-Aldrich) buffer. Nitroanilineproduction was monitored using a HTS 7000+ microplate reader(PerkinElmer, Uberlingen, Germany). The K_(i)-values were calculated vianon-linear regression using the enzyme kinetic program Grafit 4.016(Erithacus Ltd, UK).

For a reversible competitive inhibition is to assumed:$v_{i} = \frac{V_{\max}*K_{m}}{\lbrack S\rbrack + {K_{m}\left( {1 + \frac{\lbrack I\rbrack}{K_{i}}} \right)}}$

Legend.

-   -   [I] inhibitor concentration    -   K_(i) inhibition constant

Example 3

MALDI-TOF Approach

In order to investigate directly the influence of the test compoundsTFTSDY, TFTDDY and H-Ser-D-Glu-Thr-Gly-D-Val-D-Lys-D-Val-OH on the DPIV-catalyzed peptide hydrolysis the MALDI-TOF assay was used.

As described before (determination of t_(1/2)) DP IV and the testcompounds were preincubated and the reaction was started by adding theenzyme/hexapeptide mixture to substrate/buffer mix. The control reactionmixture consisted of buffer, enzyme and substrate. From the curves ofthe first order exponential the initial rate (v_(i)) for the control andthe reversible inhibited reaction was calculated.

For the uninfluenced reaction the Michaelis-Menten-equation was used.

-   -   V_(i) was calculated from plotting the relative substrate        concentration versus time.    -   K_(m) is given, also the substrate concentration.        $v_{i} = \frac{V_{\max}*K_{m}}{K_{m} + \lbrack S\rbrack}$

For the reversible inhibited reaction the following reaction was used tocalculate K_(i):$v_{i} = \frac{V_{\max}*K_{m}}{\lbrack S\rbrack + {K_{m}\left( {1 + \frac{\lbrack I\rbrack}{K_{i}}} \right)}}$

Example 4

Determination of K_(m)

Experiments were carried out with a capillary zone electrophoresisapparatus (MDQ, Beckmann, Muinchen, Germany).

The reaction mixture contained 50 μl Gly-Gly (100 mM as standard), 50 μMsubstrate solved in 0.01 M sodium phosphat buffer (pH 7.6) and 10 μl DPIV (40 mU/ml) stored at 30° C. Six substrate concentrations varying from1 μM to 60 μM were measured. As running buffer 0.1 M sodium phosphatbuffer, pH 2.5 was used. A sample from the reaction mixture was injectedwith 0.5 psi over 5 s at predefined time points. Separation was carriedout in a capillary with 50 μM inner diameter and 20 cm effective length.The following separation parameters were used: Separation voltage: 16 kVSeparation time: 12 min Separation temperature: 25° C. Detection wavelength: 200 nm

The maximal rate was calculated by plotting product concentration versustime. The K_(m)-value was calculated transferrng the data in theMichaelis-Menten-equation (GraFit 4.0.16, Erithacus Ltd., UK).

Example 5

Expression, Fermentation and Purification of Human DP IV and its MutantVariants

Strains and Plasmid:

P. pastoris strain X-33 and the vector pPICαC were purchased fromInvitrogen (USA). E. coli XL-10 cells were provided from Stratagene(USA).

Plasmid Construction and DNA Sequencing

The DP IV encoding region (Δ1-36) plus his₆-tag contained in a pcDNA-3.1vector was amplified using primers DP IV-21(TCATCGATGCATCATCATCATCATCAT) and DP IV-22 (TAGGTACCGCTAAGGTAAAGAGAAAC)while implementing the restriction sites for KpnI and BspD1. Thisfragment was digested with the restriction enzymes KpnI and BspD1 aswell as the vector pPCR-ScriptCam (Stratagene, USA), afterwards vectorand PCR product were ligated and transformed into the E. coli-strainXL-10. Insertion and orientation was confirmed applying restrictionenzyme analysis and partial sequencing. That was followed by excision ofthe DP IV encoding region from the pPCR-ScriptCam vector with the samerestriction enzymes KpnI and BspD1 and its ligation into the Pichiavector pPICαC, which was also treated with the same restriction enzymesbefore.

Site Directed Mutagenesis:

Single amino acid mutations were carried out with the Quick ChangeSite-directed Mutagenesis Kit from Stratagene (USA). Following primerswere used to introduce the mutations: R310A-DP IV: DP IV-84GACATGGGCAACACAAGAAGCAATTTCTTTGCAGTGGC DP IV-85GCCACTGCAAAGAAATTGCTTCTTGTGTTGCCCATGTC R560A-DP IV: DP IV-73:GCAGACACTGTCTTCGCACTGAACTGGGCCACTTACC DP IV-74b:GGTAAGTGGCCCAGTTCAGTGCGAAGACAGTGTCTGC W629A-DP IV: DP IV-75:GCAATTTGGGGCTGGTCATAGCGAGGGTACGTAACC DP IV 76:GGTTACGTACCCTCGCTATGACCAGCCCCAAATTGC.Transformation of P. pastoris X-33:

The vector pPICαC containing the DP IV-variants was linearized using therestriction enzyme Sac I. Transformation was carried out with anelectroporation system from BioRad (Germany) according to the InvitrogenPichia expression kit manual.

Media and Buffers:

YPD, BMMY, and BMGY for shake flask expression were prepared asdescribed in the Invitrogen Pichia expression kit manual using reagentsobtained from Difco. Media for fermentation were composed as describedin the Invitrogen Pichia fermentation process guidelines using chemicalspurchased from Sigma (Deisenhofen, Germany).

Small-Scale Expression Studies:

Single colonies were grown in BMGY at 250 rpm, 28° C. overnight.Induction of gene expression was initiated after a media exchange toBMMY. DP IV activity in the expression medium was assayed after 48hours. Clones displaying highest activity were further monitored in ashaking flask culture (15 ml BMGY and 15 ml BMMY respectively) regardinggrowth rate and expression rate.

Fermentation:

The clone displaying the highest DP IV activity was used to inoculate 5ml of BMGY. After 16-18 h of growth at 250 rpm and 28° C. 1 ml of theculture was used to start a 200 ml BMGY flask shake preculture. Thecells were grown for 16-18 h at 28° C. A 21 fermentation was startedwith the 200 ml inoculum according to the Invitrogen Pichia fermentationprocess guidelines.

Purification of DP IV

Expression medium was centrifuged at 40,000*g for 20 minutes to pelletthe yeast cells. The supernatant was filtered to remove any residualsolids using a 45 μM cellulose acetate filter from Satorius (Germany).Medium was adjusted to pH 7,6 while adding 300 mM NaCl and 50 mM sodiumphosphate buffer.

Affinity chromatography was carried out at 4° C. with a Ni-NTA sepharosecolumn (Qiagen, Germany). The column was pre-equilibrated with 300 mMNaCl, 50 mM NaH₂PO₄-buffer pH 7,6. The enzyme was eluted with 250 mMimidazole. DP IV assay and SDS-PAGE monitored the purification process.The fractions with the highest DP IV content was further concentrated byultra-filtration in an Amicon apparatus (cut off 10 kDa) to 0,5 ml.

Gel Filtration:

The 0.5 ml ultra-filtrate were applied to a Superdex 200 HiLoad 26/60column (Pharmacia, Upsalla, Sweden) with a flow rate at 0.25 ml /minusing a 300 mM NaCl, 50 mM NaH₂PO₄-buffer pH 7,6 at 4° C. Thepurification process was monitored via SDS-PAGE and activity assay.

DP IV Assay:

DP IV activity assays were performed spectrofluorimetrically usingH-Gly-Pro-AMC (Bachem, Heidelberg, Germany) as substrate and a 0.1MHEPES buffer pH 7.6 plus 0.05 M NaCl (Sigma, Deisenhofen, Germany) whilemonitoring the releasing of AMC by DP IV (λ_(excitation)=380 nm;λ_(emission)=460 nm).

SDS-PAGE Analysis:

Proteins were analysed by SDS-PAGE using 12% separating gels with 3%stacking gel. Gels were stained applying Coomassie brilliant blue R-250.

Protein Determination:

Protein concentrations were determined using the BioRad (Germany)Bradford assay kit according to the instructions of the manufacturer.

Western Blot Analysis:

Analytical gel electrophoreses in SDS-polyacrylamid gels were performedaccording to Laemmli [1] with seperation gels containing 12% acrylamide.The seperated proteins were transferred to a nitrocellulose membrane(Schleicher&Schuell, Germany) following standard procedures. To detecthis-tagged protein a penta-his-tag-antibody and a secondary antibodyprovided from Qiagen (Germany) (1:2000) was used. Chemo-luminescence wasassayed according to the manufacturers protocol (SuperSignal™ West Pico,PIERCE).

Substrates:

All investigated bioactive peptides were obtained from Bachem(Heidelberg, Germany), with exception of glucagon, GIP and its analogsand fragments. These peptides were synthesized at applicant'slaboratories.

Example 6

Synthesis of DP IV-Substrates

Glucagon, GIP and the GIP analogs were synthesized with an automatedsynthesizer SYMPHONY (RAININ) using a modified Fmoc-protocol. Cycleswere modified by using double couplings from the 15^(th) amino acid fromthe C-terminus of the peptide with five-fold excess of Fmoc-amino acidsand coupling reagent. The peptide couplings were performed byTBTU/NMM-activation using a 0.23 mmol substituted NovaSyn TGR-resin orthe corresponding preloaded Wang-resin at 25 μmol scale. The cleavagefrom the resin was carried out by a cleavage-cocktail consisting of94.5% TFA, 2.5% water, 2.5% EDT and 1% TIS.

Analytical and preparative HPLC were performed by using differentgradients on the LiChrograph HPLC system of Merck-Hitachi. The gradientswere made up from two solvents: (A) 0.1% TFA in H₂O and (B) 0.1% TFA inacetonitrile. Analytical HPLC were performed under the followingconditions: solvents were run (1 ml/min) through a 125-4 NucleosilRP18-column, over a gradient from 5%-50% B over 15 min and then up to 95% B until 20 min, with UV detection (λ=220 nm). Purification of thepeptides was carried out by preparative HPLC on either a 250-20Nucleosil 100 RP8-colunm or a 250-10 LiChrospher 300 RP18-column (flowrate 6 ml/min, 220 nm) under various conditions depending on peptidechain length. For the identification of the peptide analogues, laserdesorption mass spectrometry was employed using the HP G2025 MALDI-TOFsystem of Hewlett-Packard.

Example 7

Computer-assisted Model for Specificity Examinations of Proline-SpecificProteases

By means of homology modeling approaches a tertiary-structure-models ofhuman DP IV and porcine DP IV have been developed.

The structure of prolyl oligopeptidase (Fülöbp, V., et al. (1998) ProlylOligopeptidase: An unusual β-propeller domain regulates proteolysis.Cell 94, 161-170) (Brookhaven Protein Data Bank entry: 1 qfm) was usedas a target to model the structure of DP IV.

COMPOSER (Blundell, T. L.; Sibanda, B. L.; Sternberg, M. J. E.;Thornton, J. M. Knowledge-based prediction of protein structures and thedesign of novel molecules. Nature 1987, 326, 347-352; Blundell, T. L.;Carney, D.; Gardner, S.; Hayes, F.; Howlin, B.; Hubbard, T.; Overington,J.; Singh, D. A.; Sibanda, B. L.; Sutcliffe, M. Knowledge-based proteinmodelling and design. Eur. J. Biochem. 1988, 172, 5 13-520) a programfor homology modeling which is included in the molecular graphicsprogram package SYBYL (TRIPOS Associates Inc., 1699 S. Hanley Road,Suite 303, St. Louis, Mo. 63144) (TRIPOS Associates Inc.) was used togenerate the model of DP IV. The amino acid sequences were aligned usingthe BLOSUM30 matrix (Henikoff, S.; Henikoff, J. G. Amino acidsubstitution matrices from protein blocks. Proc. Natl. Acad. Sci. USA,(1992), 89, 10915-10919). Afterwards, the modeling procedure consistedof the following steps: structurally conserved regions (SCRs) wereidentified and a framework of conserved regions was defined as meanpositions of structurally equivalent C□-atoms. Structurally variableregions (SVRs, loops) were selected from a program attached database ofpeptide fragments in order to satisfy end-to-end distances of the SCRsalready positioned in the framework. Loops which could not be formedwith this procedure were added manually to complete the structure. Theconformations of these loops (mainly in the propeller domain) weredetermined by simulated annealing techniques in heating the temperatureto 700 K and subsequently cooling to 100 K by fixing the remaining partof the structure. This procedure was repeated 30 times. All resultinglow temperature structures were minimized using the Kollman all-atomforce field (Weiner, S. J.; Kollman, P. A.; Case, D. A.; Singh, U. C.;Ghi, C.; Alagona, G.; Profeta, S.; Weiner, P. A new Force Field formolecular mechanical simulation of nucleic acids and proteins, J. Am.Chem. Soc., 1984, 106,765-784). Loop conformations with the lowestenergy which fulfill all criteria by analyzing the stereo-chemicalquality of the protein structure by means of PROCHECK (Laskowski, R. A.et al. (1993) PROCHECK: a program to check the stereochemical quality ofprotein structures, J. Appl. Cryst. 26, 283-289) were used.

Small molecule ligands such as substrates of the typeXaa-Pro-p-Nitroanilide were docked with the “automatic” docking programGOLD (C. Bissantz, G. Folkers, D. Rognan; J. Med. Chem. 43, 4759-4767,2000) to the catalytically active site of DP IV to inspect and analyzethe principal correctness of the tertiary structure. Ligands such as GIPor glucagon and longer peptides of the GRF family were docked byapplication of molecular dynamics simulations. These simulations werestarted to form a random conformation of these compounds, manualpositioned at the outer side of the pore formed by the propeller domain.A low force constant between the protonated N-terminus of the ligandsand the side chain of Glu668, which is proposed to be the responsibleresidue for the recognition of the N-terminus of DP IV was added.Molecular dynamics simulations at 300 K for 100 ps using the Kollmanall-atom force field were performed by fixing the backbone atoms of DPIV. All these longer peptides reached the catalytically active site(amino acid position S630), showing that ligands are penetrating throughthe propeller domain to dock to the active site. The resulting dockingstructures were optimized and subsequently analyzed to define the socalled second binding site of DP IV-substrates.

Example 8

Validation of the Computer-Assisted Model of DP IV

Glycosylation Sites

The following residues are assumed to be glycosylated and are thereforeplaced at the surface of the protein: Asn85, Asn92, Asn150, Asn299,Asn229, Asn281, Asn321, Asn520 and Asn685, which are displayed in FIG.3. All these amino acid residues are accessible except Asn150 and 321,which are slightly buried but may become accessible by thermal moving ofthe loop region close to this position.

ADA-Binding Site

Site directed mutagenesis studies proved that the residues L294, V341and R343 play an important role in ADA binding to DP IV. Therefore,these residues have to be accessible too. These amino acid residues aredisplayed in FIG. 3. All these residues are situated at the surface ofthe protein and interact with ADA.

Binding of Small Inhibitors to the Active Site of DP IV

A number of Xaa-Pyrrolidine and Xaa-Proline dipeptides where docked toDP IV and their preferred interaction with the active site was examined(FIG. 4). One of the most important region is the proline recognitionsite. In POP this site is formed by the two to three amino acidresidues. In analogy to POP the proline binding pocked in DP IV isformed also by two aromatic side chains, the two tyrosine residues Y670and Y631 and by the hydrophobic residue V711.

The S2-binding site in DP IV must be responsible for the recognition ofthe protonated and positively charged N-terminus of DP IV ligands andpreferred interactions of hydrophobic residues such as Val or Ile. Themodel shows that the side chain of Glu668 is able to form a salt bridgeto the N-terminus of ligands. The recognition of the side chains isrealized by interactions with the side chains of two other tyrosineresidues (Y211 and Y330) and explains the preferred hydrophobicP2-residues of inhibitors.

Another DP IV-inhibitor, Lys(Z-nitro)-Pyrrolidine, which carries not acompletely hydrophobic P2-side chain, was also docked to DP IV. Theresult is represented in FIG. 5. In the most stable docking arrangementa scorpion like conformation of the Lys-Z-nitro group can be observed,which finally leads to the formation of a strong hydrogen bond to R453.This additional interaction in comparison to usual dipeptide relatedligands explains the high affinity and action of this compound.

Substrate Interactions and Aspects of the Catalytic Mechanism

The mode of interaction of substrates to DP IV is shown in FIG. 6.First, the substrates dock exactly in the following conformation: Ahydrogen bond is formed between the N-H group and the carbonyl group(torsional angle ψ2˜80°) of the first amino acid residue(C7-conformation) and the N-terminal amino group is turned out of a ψ1torsion of 180° to about 120°. The scissile bond or better plane of thepeptide bond to be cleaved is in a perpendicular orientation to theactive serine side chain (S630) and allows the reactive attack of theserine to the peptide bond.

Of main importance is the side chain of Y547. The phenolic hydroxylgroup forms a hydrogen bond to the carbonyl group of the scissilepeptide bond. This interaction plays a very important role in thestabilisation of the tetrahedral intermediate and therefore in thecatalytic mechanism in particular in the acylation step. Anotherinteresting finding by Heins et al. (heins et al., Biochim. Biophys.Acta, 1988, 954(2),161-169) was the fact that in the case of proline (inP1) substrates usually the deacylation is the rate limiting step except,when in P2-position an Asp is introduced. A possible docking arrangementof such a substrate is displayed in FIG. 6. The aspartate side chainforms a hydrogen bond to the phenolic OH-group of Y547. This stronginteraction prevents the cleaved dipeptide to move out of the bindingsite and thus shifts the thermodynamic equilibrium and the activationbarrier somewhat to the tetrahedral intermediate site and consequentlythe acylation rate is considerably reduced and becomes rate limiting.

Docking Behavior of Ligands with Biological Importance

It has been demonstrated that the N-terminal nonapeptide of the HIV-tatprotein shows inhibitory effects to DP IV. Docking studies of thiscompound were done with the complete DP IV model as described above. Theresulting most stable binding arrangement is shown in FIG. 7.

There are some important interactions. Similar to the already discussedinteraction of the substrate Asp-Pro-PNA D2 of Tat forms a hydrogen bondwith Y330 and furthermore as seen for Lys-Z-nitro-Pyrrolidine, D5 formsa salt bridge with R453. Further considerable hydrophobic interactionsoccur between I8 and Y330 and another salt bridge is observed betweenthe C-terminal E9 and R310 of DP IV.

Another similar peptide that was used for docking studies is theN-terminal nonapeptide of the tromboxane receptor (FIG. 8). Similarinteractions as seen for HIV-tat were detected. Additionally importantis the hydrophobic interaction between W2 and I742.

Example 9

Docking of GIP; VIP and Glucagons to DP IV

Several oligopeptides such as GIP, VIP, glucagon and others arehydrolysed by DP IV and therefore it is clear, that these substrates aredocking to DP IV and reaching the active site. Extensive dockinginvestigations by means of molecular dynamics simulations were doneusing the old model. From these studies the amino acid sequences of thehexapeptides, TFTSDY and TFTDDY and the degradation stabilizedheptapeptide H-Ser-D-Glu-Thr-Gly-D-Val-D-Lys-D-Val-OH were derived andits ability to protect oligopeptide substrates from their interactionwith a secondary binding site.

Results

The binding and hydrolysis of small dipeptide substrates were onlyslightly influenced when DP IV was preincubated with the hexapeptidesTFTSDY or TFTDDY or the degradation stabilized heptapeptideH-Ser-D-Glu-Thr-Gly-D-Val-D-Lys-D-Val-OH but the affinity of largeroligopeptides such as GIP, VIP, glucagon and others was considerablyreduced. These experiments clearly prove the existence of a secondarybinding site.

How these rather long peptides reach the active site of DP IV withoutessential steric hindrance was investigated. GIP was placed at the topof the propeller domain with the N-terminus pointing to the directionmiddle to DP IV. A small constraint (additional force constant) wasplaced between the N-terminal nitrogen atom of GIP and a carboxyl oxygenatom of E668. Then a molecular dynamics simulation over 50.000 fs at 300K was started with fixed backbone atoms of DP IV in the gas phase.Surprisingly it was shown that GIP moved in the pore rapidly without anyconsiderable steric hindrance and was indeed able to reach the activesite. Finally starting from the end structure of this “constrained”dynamic model, dynamic simulations with GIP already situated inside DPIV were repeated. The final optimized docking arrangement is shown inFIGS. 9 to 12 and the most important interactions are summarized inTables 8 to 11. TABLE 8 Most important interactions of GIP with DP IVGIP DP IV typ of interaction NT E668 salt bridge Y1—CO N710 H-bond S2—OHY631 H-bond S2—CO Y547 H-bond (Catalysis!) E3 R560 salt bridge I7 Y330hydrophob D9 R310 salt bridge Y10 W154 hydrophob I12 W157 hydrophob D15K463 (R318) salt bridge K16 E464 (E91) salt bridge

TABLE 9 Most important interactions of VIP with DP IV VIP DP IV typ ofinteraction NT E668 salt bridge H1—CO N710 H-bond H1-side chain I742hydrophob S2—OH Y631 H-bond S2—CO Y547 H-bond (catalysis!) D3 R560 saltbridge D8 R310 salt bridge Y10 W154 hydrophob Y10—CO S460 H-bond K15E464 salt bridge

TABLE 10 Most important interactions of Glucagon with DP IV Glucagon DPIV typ of interaction NT E668 salt bridge H1—CO N710 H-bond H1-sidechain I742 hydrophob A2-CO Y547 H-bond Q3 R560 H-bond T5 T152 H-bond T7Y416 H-bond S8 Y330 H-bond D9-CO Y416 H-bond D9 R310 salt bridge Y10W154 hydrophob Y13 L90 hydrophob D15 R318 salt bridge R17 E91 saltbridge

TABLE 11 Most important interactions of the hexapeptide T(5)-F-T-S-D-Ywith DP IV hexapeptide DP IV type of interaction T5 T152 H-bond T7Q153(CO-backbone) H-bond S8 S552 H-bond D9 R310 salt bridge Y10 W154hydrophobic Y10(OH) T152(OH) H-bond Y10(OH) T152(CO-backbone) H-bondY10(CT) S460(OH) H-bond

As can be seen in FIGS. 9 and 11, GIP is able to reach the active siteof DP IV, but the C-terminal tail is still at the surface of thepropeller domain.

The scissile peptide bond after Ser2 is exactly in an orientationrequired for optimal hydrolysis (FIG. 10). A number of importantinteractions which explain the affinity of GIP to DP IV were detected.These attractive interactions are summarized in Table 6. Interestingly anumber of interactions were observed, which were already discussed forother ligands (see above).

Based on these results analogous docking studies were performed withVIP, glucagon and the hexapeptide TFTSDY (FIGS. 12 to 15) The resultsare summarized by listing the most attractive interactions in Tables 7to 9.

These results prove that the oligopeptide ligands penetrate through thepropeller domain to dock to the active site. Furthermore, some highlyattractive interactions between the oligopeptide ligands and DP IV wereshown, which explain the affinity of the calculated compounds and whichwere used to predict the structure of non-peptidic ligands for thesecondary binding site of DP IV. Some preliminary structures of suchnon-peptidic ligands are provided in the description above.

Moreover, the results of these studies confirm the proposed docking ofLys-Z-nitro-Pyrrolidine, e.g. the interaction of the nitro-group withAR560. Wher the oligopeptide ligands have an Asp in third or fourthposition in their amino acid sequence, a salt bridge with R560 isformed. By docking arrangement of the hexapetide TFTSDY (FIG. 15), itwas proven that this hexapeptide indeed prevents binding of oligopeptideligands to the active site.

Example 10

Preparation of Porcine DP IV

DP IV was purified from porcine kidney. Approximately 2 kg cortex wasremoved from pig kidneys and cut in small pieces. This tissue materialwas washed with 0.9% NaCl solution overnight at 4° C. to removeremaining blood. The washed cortex was homogenized using an ultraturrax.During homogenization an equal amount of a 0.02 M sucrose solutioncontaining 0.2% Triton X-100 was added. After homogenization the DPIV-protein was released from the membrane by an 18 h autolysis step at30° C. Insoluble particles were removed by centrifugation at 15900× gfor 30 min. After a first precipitation and centrifugation step (60%(NH₄)₂SO₄-saturation, 3 h, room temperature, centrifugation: 39200× g,30 min) DP IV-activity remains in the supernatant. Second precipitationwas conducted overnight at 4° C. and 85% saturation. Aftercentrifugation the DP IV-containing pellet was dissolved in a minimalvolume of a 25 mM phosphate buffer, pH 6.8 and dialyzed against 3×21 ofthis buffer over night. After additional centrifugation (30 min, 39200×g) the solution was concentrated to approximately 45 ml using an Amiconultrafiltration cell (cut-off 100 kDa) and again centrifuged at 44000×g. A preparative size exclusion chromatography was used as secondpurification step. 15 ml of the DP IV-containing solution were appliedto a Sepharose 6B (Pharmacia) column (100 cm×2.6 cm) and eluted with thephosphate buffer, pH 6.8. The pooled fractions from 3 runs were furtherpurified by anion exchange chromatography on a DEAE-Sephacel (Pharmacia)column (17 cm×2.5 cm). For binding the 25 mM phosphate buffer pH 6.8 wasused and DP IV was eluted with a salt gradient from 39 mM to 150 mM NaClin 5 column volumes. The final separation step was a high resolutionanion exchange chromatography on a Uno Q column (6 ml, BioRad). The DPIV-containing fraction was diluted with an equal volume of H₂O andapplied to the column using a 25 mM Bis-Tris buffer pH 6.8. Elution wasperformed with a NaCl gradient from 0 to 60 mM. Final purification ofthe naturally glycosylated protein to homogeneity was achieved bypreparative isoelectric focusing using the Rotofor system (BioRad). Onerun of the above procedure yields roughly 60 mg of total protein,purified by a factor of approximately 280 and exhibiting a specificactivity of always above 42 U/mg.

Example 11

Sequencing of Porcine DP IV cDNA

To obtain the cDNA sequence of porcine DP IV, total RNA was extractedfrom porcine kidney and RT-PCR was performed as described elsewhere. Thesequence was submitted to GenBank (accession number: AY198323).

Example 12

Synthesis of p-Iodo-Phe-Pyr-CN *TFA

Synthesis of p-Iodo-Phe-Pyr-CN *TFA, an slow-tight binding inhibitor ofDP IV was performed according to known chemical protocols (Ashworth, D.M., Atrash, B., Baker, G. R., Baxter, A. J., Jenkins, P. D., Jones, D.M. & Szelke, M. (1996) Bioorg. Medicinal Chem. Letter 6, 1163-1166).

Boc-p-Iodo-Phe-Pro-NH₂. Triethylamine (163.8 ml, 1.17 mmol) was added toa solution of H-ProNH₂*HCl (118.5 mg, 0.782 mmol) in dry DMF (10 ml).Boc-p-Iodo-Phe-OSu (0.42 g, 0.86 mmol) was added in one portion and themixture stirred for 16 h under an argon atmosphere. The solvent wasevaporated and the residue treated in a standard way, i.e. the residuewas partitioned between ethylacetate (60 ml) and 0.3N KHSO₄ solution (10ml). The organic layer was further washed with saturated NaCHO₃ solution(10 ml), water (10 ml)and brine (5 ml). The solution was dried andevaporated at reduced pressure.

Boc-p-Iodo-Phe-Pyr-CN. Imidazole (38.96 mg, 0.572 mmol) was added to asolution of Boc-p-Iodo-Phe-Pro-NH₂ in dry pyridine (5 ml) under an argonatmosphere. The solution was cooled to −35° C., before the dropwiseaddition of POCl₃ (0.105 ml, 1.13 mmol). The reaction was stirred at−30° C.—to −20° C. for 60 min. The solution was then evaporated and thecrude residue subjected to column chromatography (silica gel) to yield180 mg (94%) of2-(S)-cyano-1-[tert-(butoxycarbonyl)(p-Iodo-phenylalanyl)-pyrrolidine asa colourless oil.

p-Iodo-Phe-Pyr-CN *TFA. Deprotection was carried out by stirring withtrifluoro acetic acid for 60 min. Evaporation and lyophilisation fromwater afforded 82.7 mg of 2-(S)cyano-1-(p-Iodo-phenylalanyl)pyrrolidineas a white solid.

ESI-MS: calculated 369.0, found (M+H)⁺=370.0

¹H-NMR: (D₂O), d (ppm): 1.55-1.61 (m, 1H), 1.7-1.82 (m, 1H), 1.91-2.19(m, 2H), 2.49-2.62 (m, 1H), 2.89-3.09 (m, 1H), 3.19-3.21 (m, 1H),3.21-3.34 (m, 1H), 4.31-4.39 (m, 1H), 4.61-4.69 (m, 4H), 6.91-7.00 (m,2H), 7.60-7.71 (m, 2H) ¹³C-NMR: (D₂O), d (ppm); 167.832, 131.656,118.055, 93.173, 65.934, 52.250, 47.061, 46.428, 36.322, 29154, 24.063,

Example 13

Crystallization and Crystal Transformation

Triclinic crystals were obtained at room temperature within several daysby mixing equal volumes of protein at concentration of 20 mg/ml with thereservoir solution (20-22% PEG2K, 0.1 M ammonium sulfate, and 0.1 MTris/HCl pH 8.0) using the sitting drop vapor diffusion method. Thecrystals were very sensitive towards manual handling and oxygen. Openingof the crystallization vials led to protein precipitation which was onlypartly reversible. These problems were solved by piercing the cover tapeof the crystallization plates with a syringe and immediate covering ofthe crystallization drop with perfluoropolyether (PFPE) oil. Byharvesting the crystals using a loop with humidity control most of thesurrounding mother liquor gets replaced with the PFPE oil. Crystals weremounted on an in-house rotating anode. Crystals initially diffractedvery weakly, typically below 10 Å. The humidity was then ramped downfrom 96.5% to 86.5% using a gradient of 0.5% (150 s)⁻¹ which induced aphase transition in the crystalline lattice order reflected by adramatically improved diffraction pattern. At an optimal relativehumidity crystals were flash frozen in the cold nitrogen stream andtransported to the synchrotron for data collection. For ligand complexstudies, DP IV-crystals were soaked with the inhibitor prior to thecrystal transformation procedure. Data were processed and scaled usingDENZO and SCALEPACK (Otwinowski, Z. & Minor, W. (1997) in Meth. Enzym.,eds. Carter, C. W. J. & Sweet, R. M. (Academic Press, Vol. 276, pp.307-326.).

Example 14

Structure Determination

The structure was determined by multiple wavelength anomalous dispersion(MAD) using a mercury derivative and subsequent non-crystallographicsymmetry (NCS) electron density averaging. Briefly, local two-fold axeswere determined by using the program GLRF (Tong, L. & Rossmann, M. G.(1990) Acta Cryst. A46, 783-792.). Next, a local Harker sectionperpendicular to the molecular dimer axis was cut out of thethree-dimensional anomalous Patterson map using the program MAIN (Turk,D. (1992) in Chemistry (Technische Universitat, München.), averagedalong the orthogonal local two-fold axes, and subsequently input to RSPS(Knight, S. D. (2000) Acta Cryst. D52, 42-47) for automatic localdoublet sites detection. We estimate this procedure to enhance thesignal to noise ratio for about 50-100 fold. The relative position ofthe two symmetry-related Hg-doublets was determined by translationalsearch (Knight, S. D. (2000) Acta Cryst. D52, 42-47). By construction,the resulting sites follow the local symmetry and determine thetranslational NCS parameters. After heavy atom refinement and phasing(program MLPHARE) and solvent flipping (SOLOMON) (CollaborativeComputational Project Number 4 (1994) Acta Cryst. D50, 760-763;Abrahams, J. P. & Leslie, A. G. W. (1996) Acta Cryst. D52, 30-42.),phases were extended to 2.0 Å resolution by NCS averaging using theprogram MAIN (Turk, D. (1992) in Chemistry (Technische Universitat,München.) which rendered the electron density readily interpretable,FIG. 25.

Model Building and Refinement

Using the program MAIN, we placed the catalytic domain of POP in theelectron density which served as a jump start in model building andsequence assignment of the DP IV-structure. The model was refined byusing the program CNS (Brüinger, A. T., Adams, P. D., Clore, G. M.,Delano, W. L., Gros, P., Grossekunstleve, R. W., Jiang, J. S.,Kuszewski, J., Nilges, M., Pannu, N. S., Read, R. J., Rice, L. M.,Simonson, T. & Warren, G. L. (1998) Acta Cryst. D54, 905-921.) withcurrent R-values of 21.7% (working set) and 24.9% (test set) anddeviations from ideality of 0.008 Å (bond length) and 1.4 degree (angledeviation).

1-25. (canceled)
 26. A method for the treatment of metabolic diseases in a mammal comprising co-administration to said mammal of (i) a compound capable of binding to a secondary binding site of DPIV and DPIV like enzymes and (ii) at least one anti-diabetic agent.
 27. A method for the treatment of metabolic diseases in a mammal comprising co-administration to said mammal of (i) a compound capable of binding to a secondary binding site of DPIV and DPIV like enzymes and (ii) at least one anti-diabetic agent selected from the group consisting of: DP IV inhibitors; PPAR agonists; biguanides, e.g. metformin, phenformin or buformin; protein tyrosin phosphatase-1B (PTP-1B) inhibitors; insulin and insulin mimetics; sulfonylureas and other insulin secretagogues; α-glucosidase inhibitors or acarbose; glucagon receptor agonists; GLP-1, GLP-1 mimetics, and GLP-1 receptor agonists; GLP-2, GLP-2 mimetics, and GLP-2 receptor agonists or teduglutide; exendin-4, exendin-4 mimetics, exenatide; GIP, GIP mimetics, and GIP receptor agonists; PACAP, PACAP mimetics, and PACAP receptor 3 agonists; PYY, PYY mimetics, PYY receptor agonists, and PYY receptor antagonists; one or more cholesterol lowering agents selected from the group consisting of: HMG-CoA reductase inhibitors, sequestrants, nicotinyl alkohol, nicotinic acid and salts thereof, PPARα agonists, PPARγ agonists, PPARα/γ dual agonists, inhibitors of cholesterol absorption, acyl CoA:cholesterol acyltransferase inhibitors, and antioxidants; PPARδ agonists; anti-obesity compounds; an ileal bile acid transporter inhibitor; and anti-inflammatory agents.
 28. The treatment method according to claim 27 wherein the compound is selected from the group comprising: a consensus sequence of the GRF-peptide family, TFTSDY (SEQ ID NO: 1), TFTDDY (SEQ ID NO:4), H-Ser-D-Glu-Thr-Gly-D-Val-D-Lys-D-Val-OH, and compounds of formulas a) to d):


29. The treatment method according to claim 27 wherein the anti-diabetic agent is selected from DPIV inhibitors, metformin, exenatide, exendin-4, acarbose, insulin, and sulfonylureas.
 30. The treatment method according to claim 27 wherein the metabolic disease is selected from Syndrome X, impaired glucose tolerance, glucosuria, lipid disorders, dyslipidemia, hyperlipidemia, hypertriglyceridemia, hypercholesterolemia, low HDL levels, high LDL levels, metabolic acidosis, hyperglycemia, diabetes mellitus, diabetic neuropathy and nephropathy and of sequelae caused by diabetes mellitus in mammals, metabolism-related hypertension and cardiovascular sequelae caused by hypertension in mammals.
 31. The treatment method according to claim 27 for the prophylaxis and/or treatment of skin diseases, diseases of the mucosa, autoimmune diseases, inflammatory conditions, psychosomatic, neuropsychiatric and depressive illnesses, such as anxiety, depression, sleep disorders, chronic fatigue, schizophrenia, epilepsy, nutritional disorders, spasm and chronic pain, atherosclerosis and its sequelae, vascular restenosis, irritable bowel syndrome, inflammatory bowel disease, including Crohn's disease and ulcerative colitis, other inflammatory conditions, pancreatitis, abdominal obesity, neurodegenerative disease, retinopathy, nephropathy, ovarian hyperandrogenism (polycystic ovarian syndrome), growth hormone deficiency, neutropenia, tumor metastasis, benign prostatic hypertrophy, gingivitis, osteoporosis, and other conditions.
 32. A pharmaceutical composition comprising a compound capable of binding to a secondary binding site of DP IV and DP IV like enzymes, at least one anti-diabetic agent and a pharmaceutically acceptable carrier therefore.
 33. The pharmaceutical composition of claim 32 wherein said at least one anti-diabetic agent is selected from the group consisting of: DP IV inhibitors; PPAR agonists; biguanides, e.g. metformin, phenformin or buformin; protein tyrosin phosphatase-1B (PTP-1B) inhibitors; insulin and insulin mimetics; sulfonylureas and other insulin secretagogues; α-glucosidase inhibitors or acarbose; glucagon receptor agonists; GLP-1, GLP-1 mimetics, and GLP-1 receptor agonists; GLP-2, GLP-2 mimetics, and GLP-2 receptor agonists or teduglutide; exendin-4, exendin-4 mimetics, exenatide; GIP, GIP mimetics, and GIP receptor agonists; PACAP, PACAP mimetics, and PACAP receptor 3 agonists; PYY, PYY mimetics, PYY receptor agonists, and PYY receptor antagonists; one or more cholesterol lowering agents selected from the group consisting of: HMG-CoA reductase inhibitors, sequestrants, nicotinyl alkohol, nicotinic acid and salts thereof, PPARα agonists, PPARγ agonists, PPARα/γ dual agonists, inhibitors of cholesterol absorption, acyl CoA:cholesterol acyltransferase inhibitors, and antioxidants; PPARδ agonists; anti-obesity compounds; an ileal bile acid transporter inhibitor; and anti-inflammatory agents.
 34. The pharmaceutical composition of claim 32 wherein the compound is selected from the group comprising: a consensus sequence of the GRF-peptide family, TFTSDY (SEQ ID NO: 1), TFTDDY (SEQ ID NO:4), H-Ser-D-Glu-Thr-Gly-D-Val-D-Lys-D-Val-OH, and compounds of formulas a) to d):


35. The pharmaceutical composition of claim 32 wherein said compound is TFTSDY (SEQ ID NO:)1 or TFTDDY (SEQ ID NO:4).
 36. The pharmaceutical composition of claim 32 wherein said compound is H-Ser-D-Glu-Thr-Gly-D-Val-D-Lys-D-Val-OH.
 37. The pharmaceutical composition of claim 32 wherein said compound capable of binding to a secondary binding site of DP IV and/or DP IV-like enzymes modulates the selectivity and/or activity of DP IV or DP IV-like enzymes in a mammal.
 38. The pharmaceutical composition of claim 32 wherein said compound capable of binding to a secondary binding site of DP IV and/or DP IV-like enzymes substantially prevents of the interaction of DPIV or DPIV-like enzymes with their binding proteins in a mammal.
 39. The pharmaceutical composition of claim 32 wherein said secondary binding site of DPIV and DPIV like enzymes comprises the amino acid residues L90, E91, T152, W154, W157, R310, Y330, R318, Y416, S460, K463, E464 and R560 of DP IV.
 40. The pharmaceutical composition of claim 32 wherein said secondary binding site of DPIV and DPIV like enzymes comprises the amino acid residues Glu361 and Ile407 and Nε2 of His363 of DP IV.
 41. The treatment method according to claim 27 wherein the compound blocks the product release site of DP IV and/or DP IV-like enzymes.
 42. The treatment method according to claim 27 wherein the compound substantially prevents the tetramerization of DP IV and/or DP IV-like enzymes.
 43. The treatment method according to claim 27 wherein the compound comprises 3 to 20 amino acid residues.
 44. The treatment method according to claim 27 wherein the compound comprises 5 to 12 amino acid residues.
 45. The treatment method according to claim 27 wherein the compound comprises 5 to 7 amino acid residues. 